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 $244.37   8.562%   $265.293   $265.29   $265.30   $265.30  
  Purchase #2 $179.34   5.648%   $189.4691   $189.47   $189.45   $189.50  
  Purchase #3 $14.97   6.411%   $15.9297   $15.93   $15.95   $15.90  
  Purchase #4 $69.45   8.648%   $75.456   $75.46   $75.45   $75.50  
  Purchase #5 $92.54   12.106%   $103.7429   $103.74   $103.75   $103.70  
  Purchase #6 $105.87   7.348%   $113.6493   $113.65   $113.65   $113.60  
  Purchase #7 $166.67   8.683%   $181.142   $181.14   $181.15   $181.10  
  7 purchase totals = $873.21       $944.6820   $944.68   $944.70   $944.60