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 $244.94   8.417%   $265.5566   $265.56   $265.55   $265.60  
  Purchase #2 $78.48   7.868%   $84.6548   $84.65   $84.65   $84.70  
  Purchase #3 $102.27   7.796%   $110.243   $110.24   $110.25   $110.20  
  Purchase #4 $75.26   5.147%   $79.1336   $79.13   $79.15   $79.10  
  Purchase #5 $217.74   11.785%   $243.4007   $243.40   $243.40   $243.40  
  Purchase #6 $245.69   4.690%   $257.2129   $257.21   $257.20   $257.20  
  Purchase #7 $69.41   9.285%   $75.8547   $75.85   $75.85   $75.90  
  7 purchase totals = $1,033.79       $1,116.0563   $1,116.04   $1,116.05   $1,116.10