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 $227.94   9.520%   $249.6399   $249.64   $249.65   $249.60  
  Purchase #2 $76.91   9.453%   $84.1803   $84.18   $84.20   $84.20  
  Purchase #3 $178.98   9.776%   $196.4771   $196.48   $196.50   $196.50  
  Purchase #4 $53.92   9.533%   $59.0602   $59.06   $59.05   $59.10  
  Purchase #5 $22.55   6.281%   $23.9664   $23.97   $23.95   $24.00  
  Purchase #6 $169.98   5.302%   $178.9923   $178.99   $179.00   $179.00  
  Purchase #7 $240.68   9.308%   $263.0825   $263.08   $263.10   $263.10  
  7 purchase totals = $970.96       $1,055.3987   $1,055.40   $1,055.45   $1,055.50