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 $16.46   7.176%   $17.6412   $17.64   $17.65   $17.60  
  Purchase #2 $173.81   13.554%   $197.3682   $197.37   $197.35   $197.40  
  Purchase #3 $113.46   12.555%   $127.7049   $127.70   $127.70   $127.70  
  Purchase #4 $249.86   6.513%   $266.1334   $266.13   $266.15   $266.10  
  Purchase #5 $82.79   12.612%   $93.2315   $93.23   $93.25   $93.20  
  Purchase #6 $132.88   12.492%   $149.4794   $149.48   $149.50   $149.50  
  Purchase #7 $185.58   9.834%   $203.8299   $203.83   $203.85   $203.80  
  7 purchase totals = $954.84       $1,055.3885   $1,055.38   $1,055.45   $1,055.30