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 $125.94   12.685%   $141.9155   $141.92   $141.90   $141.90  
  Purchase #2 $176.66   8.647%   $191.9358   $191.94   $191.95   $191.90  
  Purchase #3 $62.68   3.286%   $64.7397   $64.74   $64.75   $64.70  
  Purchase #4 $64.76   3.399%   $66.9612   $66.96   $66.95   $67.00  
  Purchase #5 $203.71   5.505%   $214.9242   $214.92   $214.90   $214.90  
  Purchase #6 $162.39   10.606%   $179.6131   $179.61   $179.60   $179.60  
  Purchase #7 $73.29   9.109%   $79.966   $79.97   $79.95   $80.00  
  7 purchase totals = $869.43       $940.0555   $940.06   $940.00   $940.00