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 $241.39   9.236%   $263.6848   $263.68   $263.70   $263.70  
  Purchase #2 $105.98   8.164%   $114.6322   $114.63   $114.65   $114.60  
  Purchase #3 $135.34   13.207%   $153.2144   $153.21   $153.20   $153.20  
  Purchase #4 $226.62   12.829%   $255.6931   $255.69   $255.70   $255.70  
  Purchase #5 $230.82   11.197%   $256.6649   $256.66   $256.65   $256.70  
  Purchase #6 $70.36   6.709%   $75.0805   $75.08   $75.10   $75.10  
  Purchase #7 $207.68   8.183%   $224.6745   $224.67   $224.65   $224.70  
  7 purchase totals = $1,218.19       $1,343.6444   $1,343.62   $1,343.65   $1,343.70