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 $175.92   12.106%   $197.2169   $197.22   $197.20   $197.20  
  Purchase #2 $225.39   4.838%   $236.2944   $236.29   $236.30   $236.30  
  Purchase #3 $168.32   7.825%   $181.491   $181.49   $181.50   $181.50  
  Purchase #4 $161.65   6.489%   $172.1395   $172.14   $172.15   $172.10  
  Purchase #5 $109.84   3.387%   $113.5603   $113.56   $113.55   $113.60  
  Purchase #6 $250.85   10.175%   $276.374   $276.37   $276.35   $276.40  
  Purchase #7 $84.45   12.740%   $95.2089   $95.21   $95.20   $95.20  
  7 purchase totals = $1,176.42       $1,272.2850   $1,272.28   $1,272.25   $1,272.30