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 $19.46   11.627%   $21.7226   $21.72   $21.70   $21.70  
  Purchase #2 $100.33   7.379%   $107.7334   $107.73   $107.75   $107.70  
  Purchase #3 $18.61   9.470%   $20.3724   $20.37   $20.35   $20.40  
  Purchase #4 $105.85   10.249%   $116.6986   $116.70   $116.70   $116.70  
  Purchase #5 $158.86   10.215%   $175.0875   $175.09   $175.10   $175.10  
  Purchase #6 $111.47   8.374%   $120.8045   $120.80   $120.80   $120.80  
  Purchase #7 $118.93   13.323%   $134.775   $134.78   $134.80   $134.80  
  7 purchase totals = $633.51       $697.1940   $697.19   $697.20   $697.20