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 $197.34   10.824%   $218.7001   $218.70   $218.70   $218.70  
  Purchase #2 $90.93   7.633%   $97.8707   $97.87   $97.85   $97.90  
  Purchase #3 $24.47   6.392%   $26.0341   $26.03   $26.05   $26.00  
  Purchase #4 $119.41   9.345%   $130.5689   $130.57   $130.55   $130.60  
  Purchase #5 $184.71   9.128%   $201.5703   $201.57   $201.55   $201.60  
  Purchase #6 $77.34   6.229%   $82.1575   $82.16   $82.15   $82.20  
  Purchase #7 $174.99   7.565%   $188.228   $188.23   $188.25   $188.20  
  7 purchase totals = $869.19       $945.1296   $945.13   $945.10   $945.20