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 $116.54   12.537%   $131.1506   $131.15   $131.15   $131.20  
  Purchase #2 $14.37   3.327%   $14.8481   $14.85   $14.85   $14.80  
  Purchase #3 $120.36   5.814%   $127.3577   $127.36   $127.35   $127.40  
  Purchase #4 $55.90   11.275%   $62.2027   $62.20   $62.20   $62.20  
  Purchase #5 $207.84   13.399%   $235.6885   $235.69   $235.70   $235.70  
  Purchase #6 $10.99   11.160%   $12.2165   $12.22   $12.20   $12.20  
  Purchase #7 $205.99   5.505%   $217.3297   $217.33   $217.35   $217.30  
  7 purchase totals = $731.99       $800.7938   $800.80   $800.80   $800.80