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 $22.57   10.682%   $24.9809   $24.98   $25.00   $25.00  
  Purchase #2 $249.32   7.767%   $268.6847   $268.68   $268.70   $268.70  
  Purchase #3 $142.56   10.437%   $157.439   $157.44   $157.45   $157.40  
  Purchase #4 $232.36   3.359%   $240.165   $240.17   $240.15   $240.20  
  Purchase #5 $120.83   12.679%   $136.15   $136.15   $136.15   $136.20  
  Purchase #6 $195.78   3.284%   $202.2094   $202.21   $202.20   $202.20  
  Purchase #7 $55.81   4.298%   $58.2087   $58.21   $58.20   $58.20  
  7 purchase totals = $1,019.23       $1,087.8377   $1,087.84   $1,087.85   $1,087.90