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 $207.41   7.616%   $223.2063   $223.21   $223.20   $223.20  
  Purchase #2 $136.65   9.258%   $149.3011   $149.30   $149.30   $149.30  
  Purchase #3 $240.44   3.595%   $249.0838   $249.08   $249.10   $249.10  
  Purchase #4 $204.39   10.686%   $226.2311   $226.23   $226.25   $226.20  
  Purchase #5 $21.39   12.244%   $24.009   $24.01   $24.00   $24.00  
  Purchase #6 $245.93   10.601%   $272.001   $272.00   $272.00   $272.00  
  Purchase #7 $106.60   9.384%   $116.6033   $116.60   $116.60   $116.60  
  7 purchase totals = $1,162.81       $1,260.4356   $1,260.43   $1,260.45   $1,260.40