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 $236.87   9.812%   $260.1117   $260.11   $260.10   $260.10  
  Purchase #2 $96.33   4.489%   $100.6543   $100.65   $100.65   $100.70  
  Purchase #3 $226.33   4.655%   $236.8657   $236.87   $236.85   $236.90  
  Purchase #4 $221.89   11.675%   $247.7957   $247.80   $247.80   $247.80  
  Purchase #5 $120.31   4.175%   $125.3329   $125.33   $125.35   $125.30  
  Purchase #6 $23.61   8.778%   $25.6825   $25.68   $25.70   $25.70  
  Purchase #7 $247.80   6.613%   $264.187   $264.19   $264.20   $264.20  
  7 purchase totals = $1,173.14       $1,260.6298   $1,260.63   $1,260.65   $1,260.70