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 $125.92   12.380%   $141.5089   $141.51   $141.50   $141.50  
  Purchase #2 $204.65   10.392%   $225.9172   $225.92   $225.90   $225.90  
  Purchase #3 $181.26   11.353%   $201.8384   $201.84   $201.85   $201.80  
  Purchase #4 $64.38   8.356%   $69.7596   $69.76   $69.75   $69.80  
  Purchase #5 $250.58   8.652%   $272.2602   $272.26   $272.25   $272.30  
  Purchase #6 $235.34   12.571%   $264.9246   $264.92   $264.90   $264.90  
  Purchase #7 $41.90   7.649%   $45.1049   $45.10   $45.10   $45.10  
  7 purchase totals = $1,104.03       $1,221.3138   $1,221.31   $1,221.25   $1,221.30