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 $92.61   9.722%   $101.6135   $101.61   $101.60   $101.60  
  Purchase #2 $179.36   6.542%   $191.0937   $191.09   $191.10   $191.10  
  Purchase #3 $150.44   6.107%   $159.6274   $159.63   $159.65   $159.60  
  Purchase #4 $180.86   13.796%   $205.8114   $205.81   $205.80   $205.80  
  Purchase #5 $74.30   9.669%   $81.4841   $81.48   $81.50   $81.50  
  Purchase #6 $234.47   9.421%   $256.5594   $256.56   $256.55   $256.60  
  Purchase #7 $148.51   10.733%   $164.4496   $164.45   $164.45   $164.40  
  7 purchase totals = $1,060.55       $1,160.6391   $1,160.63   $1,160.65   $1,160.60