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 $244.44   11.827%   $273.3499   $273.35   $273.35   $273.30  
  Purchase #2 $229.93   9.764%   $252.3804   $252.38   $252.40   $252.40  
  Purchase #3 $214.59   11.869%   $240.0597   $240.06   $240.05   $240.10  
  Purchase #4 $73.46   3.437%   $75.9848   $75.98   $76.00   $76.00  
  Purchase #5 $131.70   7.533%   $141.621   $141.62   $141.60   $141.60  
  Purchase #6 $85.56   11.360%   $95.2796   $95.28   $95.30   $95.30  
  Purchase #7 $60.92   11.546%   $67.9538   $67.95   $67.95   $68.00  
  7 purchase totals = $1,040.60       $1,146.6292   $1,146.62   $1,146.65   $1,146.70