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 $205.90   12.759%   $232.1708   $232.17   $232.15   $232.20  
  Purchase #2 $150.59   12.113%   $168.831   $168.83   $168.85   $168.80  
  Purchase #3 $57.65   4.365%   $60.1664   $60.17   $60.15   $60.20  
  Purchase #4 $61.26   3.193%   $63.216   $63.22   $63.20   $63.20  
  Purchase #5 $93.59   7.480%   $100.5905   $100.59   $100.60   $100.60  
  Purchase #6 $126.87   9.149%   $138.4773   $138.48   $138.50   $138.50  
  Purchase #7 $184.40   5.235%   $194.0533   $194.05   $194.05   $194.10  
  7 purchase totals = $880.26       $957.5053   $957.51   $957.50   $957.60