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 $30.62   4.841%   $32.1023   $32.10   $32.10   $32.10  
  Purchase #2 $156.51   10.211%   $172.4912   $172.49   $172.50   $172.50  
  Purchase #3 $225.43   10.873%   $249.941   $249.94   $249.95   $249.90  
  Purchase #4 $238.77   7.126%   $255.7848   $255.78   $255.80   $255.80  
  Purchase #5 $168.51   11.634%   $188.1145   $188.11   $188.10   $188.10  
  Purchase #6 $129.71   6.623%   $138.3007   $138.30   $138.30   $138.30  
  Purchase #7 $182.33   13.831%   $207.5481   $207.55   $207.55   $207.50  
  7 purchase totals = $1,131.88       $1,244.2826   $1,244.27   $1,244.30   $1,244.20