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 $174.88   10.359%   $192.9958   $193.00   $193.00   $193.00  
  Purchase #2 $94.91   10.213%   $104.6032   $104.60   $104.60   $104.60  
  Purchase #3 $119.61   10.302%   $131.9322   $131.93   $131.95   $131.90  
  Purchase #4 $85.50   13.766%   $97.2699   $97.27   $97.25   $97.30  
  Purchase #5 $103.87   9.345%   $113.5767   $113.58   $113.60   $113.60  
  Purchase #6 $153.77   6.613%   $163.9388   $163.94   $163.95   $163.90  
  Purchase #7 $170.25   11.425%   $189.7011   $189.70   $189.70   $189.70  
  7 purchase totals = $902.79       $994.0177   $994.02   $994.05   $994.00