Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $141.95   4.810%   $148.7778   $148.78   $148.80   $148.80  
  Purchase #2 $171.42   11.691%   $191.4607   $191.46   $191.45   $191.50  
  Purchase #3 $191.67   5.816%   $202.8175   $202.82   $202.80   $202.80  
  Purchase #4 $155.65   11.282%   $173.2104   $173.21   $173.20   $173.20  
  Purchase #5 $148.78   4.484%   $155.4513   $155.45   $155.45   $155.50  
  Purchase #6 $217.36   12.631%   $244.8147   $244.81   $244.80   $244.80  
  Purchase #7 $237.91   12.286%   $267.1396   $267.14   $267.15   $267.10  
  7 purchase totals = $1,264.74       $1,383.6720   $1,383.67   $1,383.65   $1,383.70