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 $55.95   7.765%   $60.2945   $60.29   $60.30   $60.30  
  Purchase #2 $26.33   7.645%   $28.3429   $28.34   $28.35   $28.30  
  Purchase #3 $187.27   4.705%   $196.0811   $196.08   $196.10   $196.10  
  Purchase #4 $243.77   10.122%   $268.4444   $268.44   $268.45   $268.40  
  Purchase #5 $119.71   11.477%   $133.4491   $133.45   $133.45   $133.40  
  Purchase #6 $207.33   10.856%   $229.8377   $229.84   $229.85   $229.80  
  Purchase #7 $48.67   6.722%   $51.9416   $51.94   $51.95   $51.90  
  7 purchase totals = $889.03       $968.3913   $968.38   $968.45   $968.20