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 $59.86   5.732%   $63.2912   $63.29   $63.30   $63.30  
  Purchase #2 $77.89   7.256%   $83.5417   $83.54   $83.55   $83.50  
  Purchase #3 $224.84   10.245%   $247.8749   $247.87   $247.85   $247.90  
  Purchase #4 $6.38   8.787%   $6.9406   $6.94   $6.95   $6.90  
  Purchase #5 $98.95   10.151%   $108.9944   $108.99   $109.00   $109.00  
  Purchase #6 $100.81   3.737%   $104.5773   $104.58   $104.60   $104.60  
  Purchase #7 $164.25   11.681%   $183.436   $183.44   $183.45   $183.40  
  7 purchase totals = $732.98       $798.6561   $798.65   $798.70   $798.60