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 $217.98   6.667%   $232.5127   $232.51   $232.50   $232.50  
  Purchase #2 $56.31   4.667%   $58.938   $58.94   $58.95   $58.90  
  Purchase #3 $150.50   13.234%   $170.4172   $170.42   $170.40   $170.40  
  Purchase #4 $57.54   11.577%   $64.2014   $64.20   $64.20   $64.20  
  Purchase #5 $242.68   4.501%   $253.603   $253.60   $253.60   $253.60  
  Purchase #6 $77.72   6.819%   $83.0197   $83.02   $83.00   $83.00  
  Purchase #7 $241.99   4.648%   $253.2377   $253.24   $253.25   $253.20  
  7 purchase totals = $1,044.72       $1,115.9297   $1,115.93   $1,115.90   $1,115.80