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 $223.67   11.852%   $250.1794   $250.18   $250.20   $250.20  
  Purchase #2 $47.53   9.696%   $52.1385   $52.14   $52.15   $52.10  
  Purchase #3 $55.54   6.537%   $59.1706   $59.17   $59.15   $59.20  
  Purchase #4 $221.78   10.337%   $244.7054   $244.71   $244.70   $244.70  
  Purchase #5 $51.57   6.275%   $54.806   $54.81   $54.80   $54.80  
  Purchase #6 $213.71   11.842%   $239.0175   $239.02   $239.00   $239.00  
  Purchase #7 $138.66   10.818%   $153.6602   $153.66   $153.65   $153.70  
  7 purchase totals = $952.46       $1,053.6776   $1,053.69   $1,053.65   $1,053.70