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 $246.73   3.735%   $255.9454   $255.95   $255.95   $255.90  
  Purchase #2 $199.95   12.849%   $225.6416   $225.64   $225.65   $225.60  
  Purchase #3 $225.52   3.497%   $233.4064   $233.41   $233.40   $233.40  
  Purchase #4 $147.42   4.184%   $153.5881   $153.59   $153.60   $153.60  
  Purchase #5 $116.38   11.220%   $129.4378   $129.44   $129.45   $129.40  
  Purchase #6 $117.33   11.157%   $130.4205   $130.42   $130.40   $130.40  
  Purchase #7 $59.83   8.487%   $64.9078   $64.91   $64.90   $64.90  
  7 purchase totals = $1,113.16       $1,193.3476   $1,193.36   $1,193.35   $1,193.20