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 $84.64   8.832%   $92.1154   $92.12   $92.10   $92.10  
  Purchase #2 $246.69   5.386%   $259.9767   $259.98   $260.00   $260.00  
  Purchase #3 $155.49   7.303%   $166.8454   $166.85   $166.85   $166.80  
  Purchase #4 $224.98   7.705%   $242.3147   $242.31   $242.30   $242.30  
  Purchase #5 $13.36   12.431%   $15.0208   $15.02   $15.00   $15.00  
  Purchase #6 $59.28   3.742%   $61.4983   $61.50   $61.50   $61.50  
  Purchase #7 $12.85   11.361%   $14.3099   $14.31   $14.30   $14.30  
  7 purchase totals = $797.29       $852.0812   $852.09   $852.05   $852.00