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 $68.93   6.294%   $73.2685   $73.27   $73.25   $73.30  
  Purchase #2 $85.81   9.652%   $94.0924   $94.09   $94.10   $94.10  
  Purchase #3 $134.45   6.592%   $143.3129   $143.31   $143.30   $143.30  
  Purchase #4 $225.81   7.766%   $243.3464   $243.35   $243.35   $243.30  
  Purchase #5 $82.76   6.214%   $87.9027   $87.90   $87.90   $87.90  
  Purchase #6 $135.34   8.310%   $146.5868   $146.59   $146.60   $146.60  
  Purchase #7 $48.85   13.113%   $55.2557   $55.26   $55.25   $55.30  
  7 purchase totals = $781.95       $843.7654   $843.77   $843.75   $843.80