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 $200.32   13.442%   $227.247   $227.25   $227.25   $227.20  
  Purchase #2 $197.64   12.498%   $222.341   $222.34   $222.35   $222.30  
  Purchase #3 $166.66   4.130%   $173.5431   $173.54   $173.55   $173.50  
  Purchase #4 $203.45   3.799%   $211.1791   $211.18   $211.20   $211.20  
  Purchase #5 $95.35   9.398%   $104.311   $104.31   $104.30   $104.30  
  Purchase #6 $129.96   12.440%   $146.127   $146.13   $146.15   $146.10  
  Purchase #7 $194.77   3.777%   $202.1265   $202.13   $202.15   $202.10  
  7 purchase totals = $1,188.15       $1,286.8747   $1,286.88   $1,286.95   $1,286.70