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 $58.53   10.426%   $64.6323   $64.63   $64.65   $64.60  
  Purchase #2 $94.29   6.616%   $100.5282   $100.53   $100.55   $100.50  
  Purchase #3 $92.91   3.381%   $96.0513   $96.05   $96.05   $96.10  
  Purchase #4 $24.62   6.132%   $26.1297   $26.13   $26.15   $26.10  
  Purchase #5 $193.93   10.522%   $214.3353   $214.34   $214.35   $214.30  
  Purchase #6 $235.43   5.600%   $248.6141   $248.61   $248.60   $248.60  
  Purchase #7 $247.35   9.480%   $270.7988   $270.80   $270.80   $270.80  
  7 purchase totals = $947.06       $1,021.0897   $1,021.09   $1,021.15   $1,021.00