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 $170.75   6.385%   $181.6524   $181.65   $181.65   $181.70  
  Purchase #2 $90.46   7.666%   $97.3947   $97.39   $97.40   $97.40  
  Purchase #3 $72.98   11.736%   $81.5449   $81.54   $81.55   $81.50  
  Purchase #4 $246.56   11.316%   $274.4607   $274.46   $274.45   $274.50  
  Purchase #5 $15.36   10.726%   $17.0075   $17.01   $17.00   $17.00  
  Purchase #6 $6.55   12.604%   $7.3756   $7.38   $7.40   $7.40  
  Purchase #7 $158.57   7.713%   $170.8005   $170.80   $170.80   $170.80  
  7 purchase totals = $761.23       $830.2363   $830.23   $830.25   $830.30