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 $111.79   12.668%   $125.9516   $125.95   $125.95   $126.00  
  Purchase #2 $40.93   5.549%   $43.2012   $43.20   $43.20   $43.20  
  Purchase #3 $10.78   8.186%   $11.6625   $11.66   $11.65   $11.70  
  Purchase #4 $89.49   6.298%   $95.1261   $95.13   $95.15   $95.10  
  Purchase #5 $217.37   8.192%   $235.177   $235.18   $235.20   $235.20  
  Purchase #6 $83.74   12.614%   $94.303   $94.30   $94.30   $94.30  
  Purchase #7 $141.64   13.457%   $160.7005   $160.70   $160.70   $160.70  
  7 purchase totals = $695.74       $766.1219   $766.12   $766.15   $766.20