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 $154.84   12.631%   $174.3978   $174.40   $174.40   $174.40  
  Purchase #2 $113.94   11.130%   $126.6215   $126.62   $126.60   $126.60  
  Purchase #3 $148.26   5.408%   $156.2779   $156.28   $156.30   $156.30  
  Purchase #4 $25.80   8.311%   $27.9442   $27.94   $27.95   $27.90  
  Purchase #5 $51.54   7.758%   $55.5385   $55.54   $55.55   $55.50  
  Purchase #6 $159.42   6.210%   $169.32   $169.32   $169.30   $169.30  
  Purchase #7 $85.46   3.246%   $88.234   $88.23   $88.25   $88.20  
  7 purchase totals = $739.26       $798.3339   $798.33   $798.35   $798.20