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 $29.86   9.367%   $32.657   $32.66   $32.65   $32.70  
  Purchase #2 $169.85   7.540%   $182.6567   $182.66   $182.65   $182.70  
  Purchase #3 $41.91   13.260%   $47.4673   $47.47   $47.45   $47.50  
  Purchase #4 $160.49   6.817%   $171.4306   $171.43   $171.45   $171.40  
  Purchase #5 $186.78   9.238%   $204.0347   $204.03   $204.05   $204.00  
  Purchase #6 $146.28   12.706%   $164.8663   $164.87   $164.85   $164.90  
  Purchase #7 $206.79   10.126%   $227.7296   $227.73   $227.75   $227.70  
  7 purchase totals = $941.96       $1,030.8422   $1,030.85   $1,030.85   $1,030.90