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 $168.96   4.483%   $176.5345   $176.53   $176.55   $176.50  
  Purchase #2 $96.83   13.472%   $109.8749   $109.87   $109.85   $109.90  
  Purchase #3 $209.56   7.347%   $224.9564   $224.96   $224.95   $225.00  
  Purchase #4 $17.37   10.818%   $19.2491   $19.25   $19.25   $19.20  
  Purchase #5 $204.28   11.137%   $227.0307   $227.03   $227.05   $227.00  
  Purchase #6 $175.32   13.256%   $198.5604   $198.56   $198.55   $198.60  
  Purchase #7 $150.68   5.292%   $158.654   $158.65   $158.65   $158.70  
  7 purchase totals = $1,023.00       $1,114.8600   $1,114.85   $1,114.85   $1,114.90