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 $181.73   13.146%   $205.6202   $205.62   $205.60   $205.60  
  Purchase #2 $93.55   4.581%   $97.8355   $97.84   $97.85   $97.80  
  Purchase #3 $76.78   11.658%   $85.731   $85.73   $85.75   $85.70  
  Purchase #4 $168.86   4.148%   $175.8643   $175.86   $175.85   $175.90  
  Purchase #5 $220.30   5.389%   $232.172   $232.17   $232.15   $232.20  
  Purchase #6 $68.26   3.564%   $70.6928   $70.69   $70.70   $70.70  
  Purchase #7 $101.67   7.402%   $109.1956   $109.20   $109.20   $109.20  
  7 purchase totals = $911.15       $977.1114   $977.11   $977.10   $977.10