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 $188.69   3.659%   $195.5942   $195.59   $195.60   $195.60  
  Purchase #2 $239.70   9.863%   $263.3416   $263.34   $263.35   $263.30  
  Purchase #3 $80.96   12.399%   $90.9982   $91.00   $91.00   $91.00  
  Purchase #4 $122.43   10.666%   $135.4884   $135.49   $135.50   $135.50  
  Purchase #5 $213.92   7.310%   $229.5576   $229.56   $229.55   $229.60  
  Purchase #6 $116.33   11.242%   $129.4078   $129.41   $129.40   $129.40  
  Purchase #7 $233.83   12.822%   $263.8117   $263.81   $263.80   $263.80  
  7 purchase totals = $1,195.86       $1,308.1995   $1,308.20   $1,308.20   $1,308.20