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 $108.92   6.518%   $116.0194   $116.02   $116.00   $116.00  
  Purchase #2 $185.91   7.393%   $199.6543   $199.65   $199.65   $199.70  
  Purchase #3 $97.90   6.523%   $104.286   $104.29   $104.30   $104.30  
  Purchase #4 $141.68   12.338%   $159.1605   $159.16   $159.15   $159.20  
  Purchase #5 $202.94   5.121%   $213.3326   $213.33   $213.35   $213.30  
  Purchase #6 $215.56   3.671%   $223.4732   $223.47   $223.45   $223.50  
  Purchase #7 $229.27   11.577%   $255.8126   $255.81   $255.80   $255.80  
  7 purchase totals = $1,182.18       $1,271.7386   $1,271.73   $1,271.70   $1,271.80