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 $68.64   12.129%   $76.9653   $76.97   $76.95   $77.00  
  Purchase #2 $54.67   7.844%   $58.9583   $58.96   $58.95   $59.00  
  Purchase #3 $68.90   10.156%   $75.8975   $75.90   $75.90   $75.90  
  Purchase #4 $81.37   8.201%   $88.0432   $88.04   $88.05   $88.00  
  Purchase #5 $57.28   12.188%   $64.2613   $64.26   $64.25   $64.30  
  Purchase #6 $198.98   8.426%   $215.7461   $215.75   $215.75   $215.70  
  Purchase #7 $166.80   3.793%   $173.1267   $173.13   $173.15   $173.10  
  7 purchase totals = $696.64       $752.9984   $753.01   $753.00   $753.00