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 $30.62   9.258%   $33.4548   $33.45   $33.45   $33.50  
  Purchase #2 $241.87   11.771%   $270.3405   $270.34   $270.35   $270.30  
  Purchase #3 $160.69   11.707%   $179.502   $179.50   $179.50   $179.50  
  Purchase #4 $88.56   6.559%   $94.3687   $94.37   $94.35   $94.40  
  Purchase #5 $13.87   13.677%   $15.767   $15.77   $15.75   $15.80  
  Purchase #6 $69.47   5.169%   $73.0609   $73.06   $73.05   $73.10  
  Purchase #7 $98.85   7.699%   $106.4605   $106.46   $106.45   $106.50  
  7 purchase totals = $703.93       $772.9544   $772.95   $772.90   $773.10