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 $193.73   5.311%   $204.019   $204.02   $204.00   $204.00  
  Purchase #2 $137.45   11.712%   $153.5481   $153.55   $153.55   $153.50  
  Purchase #3 $66.46   9.668%   $72.8854   $72.89   $72.90   $72.90  
  Purchase #4 $137.84   3.203%   $142.255   $142.26   $142.25   $142.30  
  Purchase #5 $96.55   8.332%   $104.5945   $104.59   $104.60   $104.60  
  Purchase #6 $240.62   5.481%   $253.8084   $253.81   $253.80   $253.80  
  Purchase #7 $7.69   13.643%   $8.7391   $8.74   $8.75   $8.70  
  7 purchase totals = $880.34       $939.8495   $939.86   $939.85   $939.80