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 $11.27   3.817%   $11.7002   $11.70   $11.70   $11.70  
  Purchase #2 $110.78   13.845%   $126.1175   $126.12   $126.10   $126.10  
  Purchase #3 $160.47   5.642%   $169.5237   $169.52   $169.50   $169.50  
  Purchase #4 $43.67   5.271%   $45.9718   $45.97   $45.95   $46.00  
  Purchase #5 $223.42   8.127%   $241.5773   $241.58   $241.60   $241.60  
  Purchase #6 $65.28   5.632%   $68.9566   $68.96   $68.95   $69.00  
  Purchase #7 $248.38   13.221%   $281.2183   $281.22   $281.20   $281.20  
  7 purchase totals = $863.27       $945.0654   $945.07   $945.00   $945.10