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 $161.97   11.494%   $180.5868   $180.59   $180.60   $180.60  
  Purchase #2 $242.34   5.212%   $254.9708   $254.97   $254.95   $255.00  
  Purchase #3 $115.36   11.548%   $128.6818   $128.68   $128.70   $128.70  
  Purchase #4 $108.94   9.246%   $119.0126   $119.01   $119.00   $119.00  
  Purchase #5 $198.50   12.467%   $223.247   $223.25   $223.25   $223.20  
  Purchase #6 $91.94   4.740%   $96.298   $96.30   $96.30   $96.30  
  Purchase #7 $16.96   8.714%   $18.4379   $18.44   $18.45   $18.40  
  7 purchase totals = $936.01       $1,021.2349   $1,021.24   $1,021.25   $1,021.20