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 $115.85   9.107%   $126.4005   $126.40   $126.40   $126.40  
  Purchase #2 $177.60   10.327%   $195.9408   $195.94   $195.95   $195.90  
  Purchase #3 $19.40   13.434%   $22.0062   $22.01   $22.00   $22.00  
  Purchase #4 $197.68   4.215%   $206.0122   $206.01   $206.00   $206.00  
  Purchase #5 $250.72   5.240%   $263.8577   $263.86   $263.85   $263.90  
  Purchase #6 $194.85   13.349%   $220.8605   $220.86   $220.85   $220.90  
  Purchase #7 $89.77   3.839%   $93.2163   $93.22   $93.20   $93.20  
  7 purchase totals = $1,045.87       $1,128.2942   $1,128.30   $1,128.25   $1,128.30