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 $166.65   10.802%   $184.6515   $184.65   $184.65   $184.70  
  Purchase #2 $61.25   4.712%   $64.1361   $64.14   $64.15   $64.10  
  Purchase #3 $193.59   12.313%   $217.4267   $217.43   $217.45   $217.40  
  Purchase #4 $191.32   5.202%   $201.2725   $201.27   $201.25   $201.30  
  Purchase #5 $46.35   7.802%   $49.9662   $49.97   $49.95   $50.00  
  Purchase #6 $116.52   11.576%   $130.0084   $130.01   $130.00   $130.00  
  Purchase #7 $96.28   11.264%   $107.125   $107.13   $107.15   $107.10  
  7 purchase totals = $871.96       $954.5864   $954.60   $954.60   $954.60