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 $202.89   13.819%   $230.9274   $230.93   $230.95   $230.90  
  Purchase #2 $93.26   4.201%   $97.1779   $97.18   $97.20   $97.20  
  Purchase #3 $68.39   5.423%   $72.0988   $72.10   $72.10   $72.10  
  Purchase #4 $201.73   4.410%   $210.6263   $210.63   $210.65   $210.60  
  Purchase #5 $138.67   10.108%   $152.6868   $152.69   $152.70   $152.70  
  Purchase #6 $92.50   3.164%   $95.4267   $95.43   $95.45   $95.40  
  Purchase #7 $174.61   13.663%   $198.467   $198.47   $198.45   $198.50  
  7 purchase totals = $972.05       $1,057.4109   $1,057.43   $1,057.50   $1,057.40