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 $49.70   10.645%   $54.9906   $54.99   $55.00   $55.00  
  Purchase #2 $226.87   6.188%   $240.9087   $240.91   $240.90   $240.90  
  Purchase #3 $144.34   3.175%   $148.9228   $148.92   $148.90   $148.90  
  Purchase #4 $30.59   9.866%   $33.608   $33.61   $33.60   $33.60  
  Purchase #5 $104.97   11.644%   $117.1927   $117.19   $117.20   $117.20  
  Purchase #6 $211.57   3.841%   $219.6964   $219.70   $219.70   $219.70  
  Purchase #7 $249.79   11.430%   $278.341   $278.34   $278.35   $278.30  
  7 purchase totals = $1,017.83       $1,093.6602   $1,093.66   $1,093.65   $1,093.60