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 $236.35   11.542%   $263.6295   $263.63   $263.65   $263.60  
  Purchase #2 $224.66   9.337%   $245.6365   $245.64   $245.65   $245.60  
  Purchase #3 $112.67   12.403%   $126.6445   $126.64   $126.65   $126.60  
  Purchase #4 $107.98   10.861%   $119.7077   $119.71   $119.70   $119.70  
  Purchase #5 $119.31   13.396%   $135.2928   $135.29   $135.30   $135.30  
  Purchase #6 $93.41   5.150%   $98.2206   $98.22   $98.20   $98.20  
  Purchase #7 $230.54   6.157%   $244.7343   $244.73   $244.75   $244.70  
  7 purchase totals = $1,124.92       $1,233.8659   $1,233.86   $1,233.90   $1,233.70