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 $245.58   12.556%   $276.415   $276.42   $276.40   $276.40  
  Purchase #2 $126.85   7.159%   $135.9312   $135.93   $135.95   $135.90  
  Purchase #3 $244.74   7.180%   $262.3123   $262.31   $262.30   $262.30  
  Purchase #4 $119.33   10.646%   $132.0339   $132.03   $132.05   $132.00  
  Purchase #5 $91.88   5.185%   $96.644   $96.64   $96.65   $96.60  
  Purchase #6 $105.98   6.215%   $112.5667   $112.57   $112.55   $112.60  
  Purchase #7 $225.61   8.490%   $244.7643   $244.76   $244.75   $244.80  
  7 purchase totals = $1,159.97       $1,260.6674   $1,260.66   $1,260.65   $1,260.60