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 $70.40   6.519%   $74.9894   $74.99   $75.00   $75.00  
  Purchase #2 $234.35   11.329%   $260.8995   $260.90   $260.90   $260.90  
  Purchase #3 $32.98   5.676%   $34.8519   $34.85   $34.85   $34.90  
  Purchase #4 $64.47   10.663%   $71.3444   $71.34   $71.35   $71.30  
  Purchase #5 $148.28   9.215%   $161.944   $161.94   $161.95   $161.90  
  Purchase #6 $18.77   11.417%   $20.913   $20.91   $20.90   $20.90  
  Purchase #7 $66.83   6.608%   $71.2461   $71.25   $71.25   $71.20  
  7 purchase totals = $636.08       $696.1883   $696.18   $696.20   $696.10