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 $90.63   5.146%   $95.2938   $95.29   $95.30   $95.30  
  Purchase #2 $96.51   11.239%   $107.3568   $107.36   $107.35   $107.40  
  Purchase #3 $10.50   8.211%   $11.3622   $11.36   $11.35   $11.40  
  Purchase #4 $250.98   7.637%   $270.1473   $270.15   $270.15   $270.10  
  Purchase #5 $87.40   6.562%   $93.1352   $93.14   $93.15   $93.10  
  Purchase #6 $54.43   13.177%   $61.6022   $61.60   $61.60   $61.60  
  Purchase #7 $199.67   6.667%   $212.982   $212.98   $213.00   $213.00  
  7 purchase totals = $790.12       $851.8795   $851.88   $851.90   $851.90