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 $34.95   3.559%   $36.1939   $36.19   $36.20   $36.20  
  Purchase #2 $230.68   12.661%   $259.8864   $259.89   $259.90   $259.90  
  Purchase #3 $179.62   10.669%   $198.7837   $198.78   $198.80   $198.80  
  Purchase #4 $14.42   13.638%   $16.3866   $16.39   $16.40   $16.40  
  Purchase #5 $183.99   11.111%   $204.4331   $204.43   $204.45   $204.40  
  Purchase #6 $182.86   6.446%   $194.6472   $194.65   $194.65   $194.60  
  Purchase #7 $11.87   10.398%   $13.1042   $13.10   $13.10   $13.10  
  7 purchase totals = $838.39       $923.4351   $923.43   $923.50   $923.40