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 $189.46   8.691%   $205.926   $205.93   $205.95   $205.90  
  Purchase #2 $53.80   11.534%   $60.0053   $60.01   $60.00   $60.00  
  Purchase #3 $43.85   7.577%   $47.1725   $47.17   $47.15   $47.20  
  Purchase #4 $86.43   8.488%   $93.7662   $93.77   $93.75   $93.80  
  Purchase #5 $70.66   5.325%   $74.4226   $74.42   $74.40   $74.40  
  Purchase #6 $171.90   8.746%   $186.9344   $186.93   $186.95   $186.90  
  Purchase #7 $201.31   12.454%   $226.3811   $226.38   $226.40   $226.40  
  7 purchase totals = $817.41       $894.6081   $894.61   $894.60   $894.60