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 $195.61   11.632%   $218.3634   $218.36   $218.35   $218.40  
  Purchase #2 $247.33   7.609%   $266.1493   $266.15   $266.15   $266.10  
  Purchase #3 $25.52   8.157%   $27.6017   $27.60   $27.60   $27.60  
  Purchase #4 $131.92   5.204%   $138.7851   $138.79   $138.80   $138.80  
  Purchase #5 $121.96   3.271%   $125.9493   $125.95   $125.95   $125.90  
  Purchase #6 $187.86   5.327%   $197.8673   $197.87   $197.85   $197.90  
  Purchase #7 $31.86   11.253%   $35.4452   $35.45   $35.45   $35.40  
  7 purchase totals = $942.06       $1,010.1613   $1,010.17   $1,010.15   $1,010.10