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 $241.59   3.316%   $249.6011   $249.60   $249.60   $249.60  
  Purchase #2 $234.36   8.577%   $254.4611   $254.46   $254.45   $254.50  
  Purchase #3 $231.54   6.540%   $246.6827   $246.68   $246.70   $246.70  
  Purchase #4 $48.50   6.635%   $51.718   $51.72   $51.70   $51.70  
  Purchase #5 $37.47   9.403%   $40.9933   $40.99   $41.00   $41.00  
  Purchase #6 $70.32   4.322%   $73.3592   $73.36   $73.35   $73.40  
  Purchase #7 $9.25   7.464%   $9.9404   $9.94   $9.95   $9.90  
  7 purchase totals = $873.03       $926.7558   $926.75   $926.75   $926.80