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 $149.63   4.712%   $156.6806   $156.68   $156.70   $156.70  
  Purchase #2 $154.98   13.355%   $175.6776   $175.68   $175.70   $175.70  
  Purchase #3 $97.72   9.224%   $106.7337   $106.73   $106.75   $106.70  
  Purchase #4 $244.63   8.293%   $264.9172   $264.92   $264.90   $264.90  
  Purchase #5 $13.55   11.855%   $15.1564   $15.16   $15.15   $15.20  
  Purchase #6 $150.90   10.592%   $166.8833   $166.88   $166.90   $166.90  
  Purchase #7 $185.72   11.187%   $206.4965   $206.50   $206.50   $206.50  
  7 purchase totals = $997.13       $1,092.5453   $1,092.55   $1,092.60   $1,092.60