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 $245.37   5.544%   $258.9733   $258.97   $258.95   $259.00  
  Purchase #2 $173.55   11.582%   $193.6506   $193.65   $193.65   $193.70  
  Purchase #3 $153.94   12.804%   $173.6505   $173.65   $173.65   $173.70  
  Purchase #4 $211.58   4.513%   $221.1286   $221.13   $221.15   $221.10  
  Purchase #5 $121.44   3.166%   $125.2848   $125.28   $125.30   $125.30  
  Purchase #6 $33.58   6.664%   $35.8178   $35.82   $35.80   $35.80  
  Purchase #7 $83.71   3.542%   $86.675   $86.68   $86.70   $86.70  
  7 purchase totals = $1,023.17       $1,095.1806   $1,095.18   $1,095.20   $1,095.30