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 $226.95   8.722%   $246.7446   $246.74   $246.75   $246.70  
  Purchase #2 $27.92   13.516%   $31.6937   $31.69   $31.70   $31.70  
  Purchase #3 $83.57   12.451%   $93.9753   $93.98   $94.00   $94.00  
  Purchase #4 $242.76   13.361%   $275.1952   $275.20   $275.20   $275.20  
  Purchase #5 $138.25   7.619%   $148.7833   $148.78   $148.80   $148.80  
  Purchase #6 $117.33   12.167%   $131.6055   $131.61   $131.60   $131.60  
  Purchase #7 $127.38   6.449%   $135.5947   $135.59   $135.60   $135.60  
  7 purchase totals = $964.16       $1,063.5923   $1,063.59   $1,063.65   $1,063.60