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 $244.36   7.820%   $263.469   $263.47   $263.45   $263.50  
  Purchase #2 $12.54   10.286%   $13.8299   $13.83   $13.85   $13.80  
  Purchase #3 $63.55   10.472%   $70.205   $70.21   $70.20   $70.20  
  Purchase #4 $31.65   8.807%   $34.4374   $34.44   $34.45   $34.40  
  Purchase #5 $97.36   6.622%   $103.8072   $103.81   $103.80   $103.80  
  Purchase #6 $250.50   8.667%   $272.2108   $272.21   $272.20   $272.20  
  Purchase #7 $130.88   5.150%   $137.6203   $137.62   $137.60   $137.60  
  7 purchase totals = $830.84       $895.5796   $895.59   $895.55   $895.50