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 $71.26   8.456%   $77.2857   $77.29   $77.30   $77.30  
  Purchase #2 $84.60   12.292%   $94.999   $95.00   $95.00   $95.00  
  Purchase #3 $84.68   9.758%   $92.9431   $92.94   $92.95   $92.90  
  Purchase #4 $35.86   11.829%   $40.1019   $40.10   $40.10   $40.10  
  Purchase #5 $72.90   12.539%   $82.0409   $82.04   $82.05   $82.00  
  Purchase #6 $116.93   8.275%   $126.606   $126.61   $126.60   $126.60  
  Purchase #7 $196.30   12.532%   $220.9003   $220.90   $220.90   $220.90  
  7 purchase totals = $662.53       $734.8769   $734.88   $734.90   $734.80