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 $112.88   12.208%   $126.6604   $126.66   $126.65   $126.70  
  Purchase #2 $52.67   8.640%   $57.2207   $57.22   $57.20   $57.20  
  Purchase #3 $181.88   10.403%   $200.801   $200.80   $200.80   $200.80  
  Purchase #4 $26.82   6.362%   $28.5263   $28.53   $28.55   $28.50  
  Purchase #5 $119.36   3.601%   $123.6582   $123.66   $123.65   $123.70  
  Purchase #6 $120.69   12.132%   $135.3321   $135.33   $135.35   $135.30  
  Purchase #7 $117.64   13.131%   $133.0873   $133.09   $133.10   $133.10  
  7 purchase totals = $731.94       $805.2860   $805.29   $805.30   $805.30