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 $226.65   8.586%   $246.1102   $246.11   $246.10   $246.10  
  Purchase #2 $170.62   13.823%   $194.2048   $194.20   $194.20   $194.20  
  Purchase #3 $221.74   6.157%   $235.3925   $235.39   $235.40   $235.40  
  Purchase #4 $131.39   5.138%   $138.1408   $138.14   $138.15   $138.10  
  Purchase #5 $229.32   10.797%   $254.0797   $254.08   $254.10   $254.10  
  Purchase #6 $21.36   13.746%   $24.2961   $24.30   $24.30   $24.30  
  Purchase #7 $130.69   8.387%   $141.651   $141.65   $141.65   $141.70  
  7 purchase totals = $1,131.77       $1,233.8751   $1,233.87   $1,233.90   $1,233.90