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 $22.87   5.638%   $24.1594   $24.16   $24.15   $24.20  
  Purchase #2 $208.33   13.624%   $236.7129   $236.71   $236.70   $236.70  
  Purchase #3 $207.92   5.399%   $219.1456   $219.15   $219.15   $219.10  
  Purchase #4 $50.96   9.584%   $55.844   $55.84   $55.85   $55.80  
  Purchase #5 $90.99   3.306%   $93.9981   $94.00   $94.00   $94.00  
  Purchase #6 $191.56   7.846%   $206.5898   $206.59   $206.60   $206.60  
  Purchase #7 $207.93   6.414%   $221.2666   $221.27   $221.25   $221.30  
  7 purchase totals = $980.56       $1,057.7164   $1,057.72   $1,057.70   $1,057.70