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 $227.53   9.818%   $249.8689   $249.87   $249.85   $249.90  
  Purchase #2 $197.84   11.689%   $220.9655   $220.97   $220.95   $221.00  
  Purchase #3 $14.88   8.202%   $16.1005   $16.10   $16.10   $16.10  
  Purchase #4 $212.26   12.485%   $238.7607   $238.76   $238.75   $238.80  
  Purchase #5 $189.46   6.521%   $201.8147   $201.81   $201.80   $201.80  
  Purchase #6 $114.83   3.783%   $119.174   $119.17   $119.15   $119.20  
  Purchase #7 $13.48   6.867%   $14.4057   $14.41   $14.40   $14.40  
  7 purchase totals = $970.28       $1,061.0900   $1,061.09   $1,061.00   $1,061.20