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 $221.97   9.655%   $243.4012   $243.40   $243.40   $243.40  
  Purchase #2 $196.36   4.566%   $205.3258   $205.33   $205.35   $205.30  
  Purchase #3 $58.63   5.554%   $61.8863   $61.89   $61.90   $61.90  
  Purchase #4 $83.37   13.761%   $94.8425   $94.84   $94.85   $94.80  
  Purchase #5 $209.58   10.534%   $231.6572   $231.66   $231.65   $231.70  
  Purchase #6 $227.94   4.179%   $237.4656   $237.47   $237.45   $237.50  
  Purchase #7 $7.47   6.288%   $7.9397   $7.94   $7.95   $7.90  
  7 purchase totals = $1,005.32       $1,082.5183   $1,082.53   $1,082.55   $1,082.50