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 $53.61   4.110%   $55.8134   $55.81   $55.80   $55.80  
  Purchase #2 $239.53   7.593%   $257.7175   $257.72   $257.70   $257.70  
  Purchase #3 $231.80   8.232%   $250.8818   $250.88   $250.90   $250.90  
  Purchase #4 $36.81   6.793%   $39.3105   $39.31   $39.30   $39.30  
  Purchase #5 $97.66   9.715%   $107.1477   $107.15   $107.15   $107.10  
  Purchase #6 $21.43   11.187%   $23.8274   $23.83   $23.85   $23.80  
  Purchase #7 $25.27   11.370%   $28.1432   $28.14   $28.15   $28.10  
  7 purchase totals = $706.11       $762.8415   $762.84   $762.85   $762.70