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 $63.47   13.397%   $71.9731   $71.97   $71.95   $72.00  
  Purchase #2 $202.29   8.272%   $219.0234   $219.02   $219.00   $219.00  
  Purchase #3 $149.49   7.570%   $160.8064   $160.81   $160.80   $160.80  
  Purchase #4 $202.96   10.708%   $224.693   $224.69   $224.70   $224.70  
  Purchase #5 $144.56   9.318%   $158.0301   $158.03   $158.05   $158.00  
  Purchase #6 $110.96   12.228%   $124.5282   $124.53   $124.55   $124.50  
  Purchase #7 $197.66   5.124%   $207.7881   $207.79   $207.80   $207.80  
  7 purchase totals = $1,071.39       $1,166.8423   $1,166.84   $1,166.85   $1,166.80