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 $63.98   8.267%   $69.2692   $69.27   $69.25   $69.30  
  Purchase #2 $225.95   8.820%   $245.8788   $245.88   $245.90   $245.90  
  Purchase #3 $32.33   9.277%   $35.3293   $35.33   $35.35   $35.30  
  Purchase #4 $192.54   11.641%   $214.9536   $214.95   $214.95   $215.00  
  Purchase #5 $52.91   6.496%   $56.347   $56.35   $56.35   $56.30  
  Purchase #6 $212.54   12.314%   $238.7122   $238.71   $238.70   $238.70  
  Purchase #7 $31.62   11.183%   $35.1561   $35.16   $35.15   $35.20  
  7 purchase totals = $811.87       $895.6462   $895.65   $895.65   $895.70