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 $9.89   5.329%   $10.417   $10.42   $10.40   $10.40  
  Purchase #2 $113.86   7.320%   $122.1946   $122.19   $122.20   $122.20  
  Purchase #3 $10.42   9.394%   $11.3989   $11.40   $11.40   $11.40  
  Purchase #4 $181.69   8.628%   $197.3662   $197.37   $197.35   $197.40  
  Purchase #5 $107.88   3.277%   $111.4152   $111.42   $111.40   $111.40  
  Purchase #6 $12.41   11.226%   $13.8031   $13.80   $13.80   $13.80  
  Purchase #7 $100.86   3.398%   $104.2872   $104.29   $104.30   $104.30  
  7 purchase totals = $537.01       $570.8822   $570.89   $570.85   $570.90