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 $176.53   11.627%   $197.0551   $197.06   $197.05   $197.10  
  Purchase #2 $209.96   8.281%   $227.3468   $227.35   $227.35   $227.30  
  Purchase #3 $37.30   11.184%   $41.4716   $41.47   $41.45   $41.50  
  Purchase #4 $65.84   9.312%   $71.971   $71.97   $71.95   $72.00  
  Purchase #5 $159.62   8.596%   $173.3409   $173.34   $173.35   $173.30  
  Purchase #6 $86.95   4.270%   $90.6628   $90.66   $90.65   $90.70  
  Purchase #7 $29.36   8.645%   $31.8982   $31.90   $31.90   $31.90  
  7 purchase totals = $765.56       $833.7464   $833.75   $833.70   $833.80