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 $160.91   13.726%   $182.9965   $183.00   $183.00   $183.00  
  Purchase #2 $65.32   11.242%   $72.6633   $72.66   $72.65   $72.70  
  Purchase #3 $86.56   3.605%   $89.6805   $89.68   $89.70   $89.70  
  Purchase #4 $227.42   13.348%   $257.776   $257.78   $257.80   $257.80  
  Purchase #5 $22.79   10.227%   $25.1207   $25.12   $25.10   $25.10  
  Purchase #6 $156.86   6.764%   $167.47   $167.47   $167.45   $167.50  
  Purchase #7 $150.39   8.669%   $163.4273   $163.43   $163.45   $163.40  
  7 purchase totals = $870.25       $959.1343   $959.14   $959.15   $959.20