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 $94.29   11.647%   $105.272   $105.27   $105.25   $105.30  
  Purchase #2 $151.57   9.409%   $165.8312   $165.83   $165.85   $165.80  
  Purchase #3 $14.73   9.755%   $16.1669   $16.17   $16.15   $16.20  
  Purchase #4 $86.40   12.441%   $97.149   $97.15   $97.15   $97.10  
  Purchase #5 $200.77   5.844%   $212.503   $212.50   $212.50   $212.50  
  Purchase #6 $142.77   5.656%   $150.8451   $150.85   $150.85   $150.80  
  Purchase #7 $72.41   6.622%   $77.205   $77.21   $77.20   $77.20  
  7 purchase totals = $762.94       $824.9722   $824.98   $824.95   $824.90