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 $163.39   7.439%   $175.5446   $175.54   $175.55   $175.50  
  Purchase #2 $238.62   11.659%   $266.4407   $266.44   $266.45   $266.40  
  Purchase #3 $82.92   11.790%   $92.6963   $92.70   $92.70   $92.70  
  Purchase #4 $177.39   4.684%   $185.6989   $185.70   $185.70   $185.70  
  Purchase #5 $23.27   6.315%   $24.7395   $24.74   $24.75   $24.70  
  Purchase #6 $112.46   8.302%   $121.7964   $121.80   $121.80   $121.80  
  Purchase #7 $167.27   12.642%   $188.4163   $188.42   $188.40   $188.40  
  7 purchase totals = $965.32       $1,055.3327   $1,055.34   $1,055.35   $1,055.20