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 $233.28   5.463%   $246.0241   $246.02   $246.00   $246.00  
  Purchase #2 $64.78   10.297%   $71.4504   $71.45   $71.45   $71.50  
  Purchase #3 $47.36   13.175%   $53.5997   $53.60   $53.60   $53.60  
  Purchase #4 $83.43   3.831%   $86.6262   $86.63   $86.65   $86.60  
  Purchase #5 $191.59   5.267%   $201.681   $201.68   $201.70   $201.70  
  Purchase #6 $60.61   6.224%   $64.3824   $64.38   $64.40   $64.40  
  Purchase #7 $250.59   5.736%   $264.9638   $264.96   $264.95   $265.00  
  7 purchase totals = $931.64       $988.7276   $988.72   $988.75   $988.80