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 $107.29   11.793%   $119.9427   $119.94   $119.95   $119.90  
  Purchase #2 $103.83   3.674%   $107.6447   $107.64   $107.65   $107.60  
  Purchase #3 $152.84   3.436%   $158.0916   $158.09   $158.10   $158.10  
  Purchase #4 $210.76   7.211%   $225.9579   $225.96   $225.95   $226.00  
  Purchase #5 $95.90   9.167%   $104.6912   $104.69   $104.70   $104.70  
  Purchase #6 $132.89   3.813%   $137.9571   $137.96   $137.95   $138.00  
  Purchase #7 $188.71   7.217%   $202.3292   $202.33   $202.35   $202.30  
  7 purchase totals = $992.22       $1,056.6144   $1,056.61   $1,056.65   $1,056.60