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 $112.93   11.181%   $125.5567   $125.56   $125.55   $125.60  
  Purchase #2 $222.78   12.531%   $250.6966   $250.70   $250.70   $250.70  
  Purchase #3 $67.98   3.778%   $70.5483   $70.55   $70.55   $70.50  
  Purchase #4 $184.98   9.741%   $202.9989   $203.00   $203.00   $203.00  
  Purchase #5 $55.99   12.843%   $63.1808   $63.18   $63.20   $63.20  
  Purchase #6 $16.77   4.807%   $17.5761   $17.58   $17.60   $17.60  
  Purchase #7 $205.41   4.112%   $213.8565   $213.86   $213.85   $213.90  
  7 purchase totals = $866.84       $944.4139   $944.43   $944.45   $944.50