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 $41.70   12.281%   $46.8212   $46.82   $46.80   $46.80  
  Purchase #2 $228.91   3.841%   $237.7024   $237.70   $237.70   $237.70  
  Purchase #3 $182.86   13.124%   $206.8585   $206.86   $206.85   $206.90  
  Purchase #4 $169.78   3.626%   $175.9362   $175.94   $175.95   $175.90  
  Purchase #5 $173.48   5.810%   $183.5592   $183.56   $183.55   $183.60  
  Purchase #6 $162.59   5.653%   $171.7812   $171.78   $171.80   $171.80  
  Purchase #7 $243.46   5.362%   $256.5143   $256.51   $256.50   $256.50  
  7 purchase totals = $1,202.78       $1,279.1730   $1,279.17   $1,279.15   $1,279.20