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 $67.69   13.219%   $76.6379   $76.64   $76.65   $76.60  
  Purchase #2 $5.66   11.505%   $6.3112   $6.31   $6.30   $6.30  
  Purchase #3 $205.98   12.128%   $230.9613   $230.96   $230.95   $231.00  
  Purchase #4 $31.46   4.826%   $32.9783   $32.98   $33.00   $33.00  
  Purchase #5 $236.82   8.345%   $256.5826   $256.58   $256.60   $256.60  
  Purchase #6 $195.40   7.361%   $209.7834   $209.78   $209.80   $209.80  
  Purchase #7 $13.26   8.397%   $14.3734   $14.37   $14.35   $14.40  
  7 purchase totals = $756.27       $827.6281   $827.62   $827.65   $827.70