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 $98.53   5.415%   $103.8654   $103.87   $103.85   $103.90  
  Purchase #2 $169.89   4.496%   $177.5283   $177.53   $177.55   $177.50  
  Purchase #3 $156.37   5.609%   $165.1408   $165.14   $165.15   $165.10  
  Purchase #4 $250.63   9.288%   $273.9085   $273.91   $273.90   $273.90  
  Purchase #5 $167.97   4.768%   $175.9788   $175.98   $176.00   $176.00  
  Purchase #6 $194.35   9.765%   $213.3283   $213.33   $213.35   $213.30  
  Purchase #7 $36.80   12.152%   $41.2719   $41.27   $41.25   $41.30  
  7 purchase totals = $1,074.54       $1,151.0220   $1,151.03   $1,151.05   $1,151.00