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 $205.67   13.677%   $233.7995   $233.80   $233.80   $233.80  
  Purchase #2 $250.52   7.254%   $268.6927   $268.69   $268.70   $268.70  
  Purchase #3 $42.97   13.447%   $48.7482   $48.75   $48.75   $48.70  
  Purchase #4 $138.82   11.411%   $154.6608   $154.66   $154.65   $154.70  
  Purchase #5 $225.78   7.268%   $242.1897   $242.19   $242.20   $242.20  
  Purchase #6 $105.99   12.114%   $118.8296   $118.83   $118.85   $118.80  
  Purchase #7 $167.44   8.182%   $181.1399   $181.14   $181.15   $181.10  
  7 purchase totals = $1,137.19       $1,248.0604   $1,248.06   $1,248.10   $1,248.00