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 $75.41   13.414%   $85.5255   $85.53   $85.55   $85.50  
  Purchase #2 $232.62   7.307%   $249.6175   $249.62   $249.60   $249.60  
  Purchase #3 $92.89   6.457%   $98.8879   $98.89   $98.90   $98.90  
  Purchase #4 $153.40   7.493%   $164.8943   $164.89   $164.90   $164.90  
  Purchase #5 $95.57   11.787%   $106.8348   $106.83   $106.85   $106.80  
  Purchase #6 $204.91   10.203%   $225.817   $225.82   $225.80   $225.80  
  Purchase #7 $116.93   3.770%   $121.3383   $121.34   $121.35   $121.30  
  7 purchase totals = $971.73       $1,052.9153   $1,052.92   $1,052.95   $1,052.80