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 $74.45   12.355%   $83.6483   $83.65   $83.65   $83.60  
  Purchase #2 $247.56   8.864%   $269.5037   $269.50   $269.50   $269.50  
  Purchase #3 $175.62   11.856%   $196.4415   $196.44   $196.45   $196.40  
  Purchase #4 $31.91   6.371%   $33.943   $33.94   $33.95   $33.90  
  Purchase #5 $193.61   10.568%   $214.0707   $214.07   $214.05   $214.10  
  Purchase #6 $166.64   9.515%   $182.4958   $182.50   $182.50   $182.50  
  Purchase #7 $66.75   10.867%   $74.0037   $74.00   $74.00   $74.00  
  7 purchase totals = $956.54       $1,054.1067   $1,054.10   $1,054.10   $1,054.00