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 $22.65   8.490%   $24.573   $24.57   $24.55   $24.60  
  Purchase #2 $144.33   12.352%   $162.1576   $162.16   $162.15   $162.20  
  Purchase #3 $43.90   12.333%   $49.3142   $49.31   $49.30   $49.30  
  Purchase #4 $130.89   13.561%   $148.64   $148.64   $148.65   $148.60  
  Purchase #5 $159.67   9.148%   $174.2766   $174.28   $174.30   $174.30  
  Purchase #6 $67.44   11.652%   $75.2981   $75.30   $75.30   $75.30  
  Purchase #7 $127.43   11.228%   $141.7378   $141.74   $141.75   $141.70  
  7 purchase totals = $696.31       $775.9973   $776.00   $776.00   $776.00