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 $47.77   11.343%   $53.1886   $53.19   $53.20   $53.20  
  Purchase #2 $142.77   7.443%   $153.3964   $153.40   $153.40   $153.40  
  Purchase #3 $226.42   13.712%   $257.4667   $257.47   $257.45   $257.50  
  Purchase #4 $232.73   12.620%   $262.1005   $262.10   $262.10   $262.10  
  Purchase #5 $50.32   3.524%   $52.0933   $52.09   $52.10   $52.10  
  Purchase #6 $190.64   6.117%   $202.3014   $202.30   $202.30   $202.30  
  Purchase #7 $62.93   8.811%   $68.4748   $68.47   $68.45   $68.50  
  7 purchase totals = $953.58       $1,049.0217   $1,049.02   $1,049.00   $1,049.10