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 $83.97   13.538%   $95.3379   $95.34   $95.35   $95.30  
  Purchase #2 $138.94   10.397%   $153.3856   $153.39   $153.40   $153.40  
  Purchase #3 $57.86   13.342%   $65.5797   $65.58   $65.60   $65.60  
  Purchase #4 $135.66   9.417%   $148.4351   $148.44   $148.45   $148.40  
  Purchase #5 $122.83   11.812%   $137.3387   $137.34   $137.35   $137.30  
  Purchase #6 $49.57   12.320%   $55.677   $55.68   $55.70   $55.70  
  Purchase #7 $185.46   6.332%   $197.2033   $197.20   $197.20   $197.20  
  7 purchase totals = $774.29       $852.9573   $852.97   $853.05   $852.90