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 $84.48   11.714%   $94.376   $94.38   $94.40   $94.40  
  Purchase #2 $94.86   10.635%   $104.9484   $104.95   $104.95   $104.90  
  Purchase #3 $108.89   12.248%   $122.2268   $122.23   $122.25   $122.20  
  Purchase #4 $189.69   6.275%   $201.593   $201.59   $201.60   $201.60  
  Purchase #5 $107.36   9.316%   $117.3617   $117.36   $117.35   $117.40  
  Purchase #6 $81.58   6.721%   $87.063   $87.06   $87.05   $87.10  
  Purchase #7 $22.43   4.161%   $23.3633   $23.36   $23.35   $23.40  
  7 purchase totals = $689.29       $750.9322   $750.93   $750.95   $751.00