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 $183.94   12.756%   $207.4034   $207.40   $207.40   $207.40  
  Purchase #2 $94.52   4.168%   $98.4596   $98.46   $98.45   $98.50  
  Purchase #3 $239.86   11.535%   $267.5279   $267.53   $267.55   $267.50  
  Purchase #4 $5.85   10.596%   $6.4699   $6.47   $6.45   $6.50  
  Purchase #5 $138.95   8.810%   $151.1915   $151.19   $151.20   $151.20  
  Purchase #6 $75.62   11.868%   $84.5946   $84.59   $84.60   $84.60  
  Purchase #7 $159.94   12.329%   $179.659   $179.66   $179.65   $179.70  
  7 purchase totals = $898.68       $995.3059   $995.30   $995.30   $995.40