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 $148.65   10.783%   $164.6789   $164.68   $164.70   $164.70  
  Purchase #2 $98.93   8.696%   $107.533   $107.53   $107.55   $107.50  
  Purchase #3 $201.62   4.369%   $210.4288   $210.43   $210.45   $210.40  
  Purchase #4 $210.90   7.114%   $225.9034   $225.90   $225.90   $225.90  
  Purchase #5 $198.88   8.377%   $215.5402   $215.54   $215.55   $215.50  
  Purchase #6 $151.90   12.511%   $170.9042   $170.90   $170.90   $170.90  
  Purchase #7 $61.82   6.494%   $65.8346   $65.83   $65.85   $65.80  
  7 purchase totals = $1,072.70       $1,160.8231   $1,160.81   $1,160.90   $1,160.70