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 $67.83   13.796%   $77.1878   $77.19   $77.20   $77.20  
  Purchase #2 $191.59   12.539%   $215.6135   $215.61   $215.60   $215.60  
  Purchase #3 $213.51   13.565%   $242.4726   $242.47   $242.45   $242.50  
  Purchase #4 $128.65   5.722%   $136.0114   $136.01   $136.00   $136.00  
  Purchase #5 $116.74   12.358%   $131.1667   $131.17   $131.15   $131.20  
  Purchase #6 $25.26   13.384%   $28.6408   $28.64   $28.65   $28.60  
  Purchase #7 $170.54   7.615%   $183.5266   $183.53   $183.55   $183.50  
  7 purchase totals = $914.12       $1,014.6194   $1,014.62   $1,014.60   $1,014.60