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 $163.66   12.564%   $184.2222   $184.22   $184.20   $184.20  
  Purchase #2 $59.30   5.716%   $62.6896   $62.69   $62.70   $62.70  
  Purchase #3 $249.67   9.282%   $272.8444   $272.84   $272.85   $272.80  
  Purchase #4 $221.30   6.188%   $234.994   $234.99   $235.00   $235.00  
  Purchase #5 $15.85   12.320%   $17.8027   $17.80   $17.80   $17.80  
  Purchase #6 $250.96   9.298%   $274.2943   $274.29   $274.30   $274.30  
  Purchase #7 $152.86   7.652%   $164.5568   $164.56   $164.55   $164.60  
  7 purchase totals = $1,113.60       $1,211.4040   $1,211.39   $1,211.40   $1,211.40