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 $96.49   9.490%   $105.6469   $105.65   $105.65   $105.60  
  Purchase #2 $219.58   11.873%   $245.6507   $245.65   $245.65   $245.70  
  Purchase #3 $82.79   9.171%   $90.3827   $90.38   $90.40   $90.40  
  Purchase #4 $12.86   11.543%   $14.3444   $14.34   $14.35   $14.30  
  Purchase #5 $230.62   7.433%   $247.762   $247.76   $247.75   $247.80  
  Purchase #6 $220.49   9.253%   $240.8919   $240.89   $240.90   $240.90  
  Purchase #7 $161.79   10.621%   $178.9737   $178.97   $178.95   $179.00  
  7 purchase totals = $1,024.62       $1,123.6523   $1,123.64   $1,123.65   $1,123.70