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 $188.63   3.270%   $194.7982   $194.80   $194.80   $194.80  
  Purchase #2 $73.83   13.181%   $83.5615   $83.56   $83.55   $83.60  
  Purchase #3 $173.93   5.366%   $183.2631   $183.26   $183.25   $183.30  
  Purchase #4 $60.34   5.314%   $63.5465   $63.55   $63.55   $63.50  
  Purchase #5 $153.57   12.333%   $172.5098   $172.51   $172.50   $172.50  
  Purchase #6 $39.91   4.567%   $41.7327   $41.73   $41.75   $41.70  
  Purchase #7 $212.65   3.523%   $220.1417   $220.14   $220.15   $220.10  
  7 purchase totals = $902.86       $959.5535   $959.55   $959.55   $959.50