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 $170.33   9.798%   $187.0189   $187.02   $187.00   $187.00  
  Purchase #2 $127.59   8.523%   $138.4645   $138.46   $138.45   $138.50  
  Purchase #3 $161.71   9.428%   $176.956   $176.96   $176.95   $177.00  
  Purchase #4 $71.26   7.293%   $76.457   $76.46   $76.45   $76.50  
  Purchase #5 $47.92   5.167%   $50.396   $50.40   $50.40   $50.40  
  Purchase #6 $50.67   4.668%   $53.0353   $53.04   $53.05   $53.00  
  Purchase #7 $61.73   13.235%   $69.9   $69.90   $69.90   $69.90  
  7 purchase totals = $691.21       $752.2277   $752.24   $752.20   $752.30