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 $58.95   12.319%   $66.2121   $66.21   $66.20   $66.20  
  Purchase #2 $68.40   7.287%   $73.3843   $73.38   $73.40   $73.40  
  Purchase #3 $225.50   6.680%   $240.5634   $240.56   $240.55   $240.60  
  Purchase #4 $178.34   5.394%   $187.9597   $187.96   $187.95   $188.00  
  Purchase #5 $147.69   5.668%   $156.0611   $156.06   $156.05   $156.10  
  Purchase #6 $77.70   6.294%   $82.5904   $82.59   $82.60   $82.60  
  Purchase #7 $214.79   9.285%   $234.7333   $234.73   $234.75   $234.70  
  7 purchase totals = $971.37       $1,041.5043   $1,041.49   $1,041.50   $1,041.60