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 $249.99   3.650%   $259.1146   $259.11   $259.10   $259.10  
  Purchase #2 $98.93   4.728%   $103.6074   $103.61   $103.60   $103.60  
  Purchase #3 $40.50   9.642%   $44.405   $44.41   $44.40   $44.40  
  Purchase #4 $97.59   6.365%   $103.8016   $103.80   $103.80   $103.80  
  Purchase #5 $157.64   8.758%   $171.4461   $171.45   $171.45   $171.40  
  Purchase #6 $168.80   13.721%   $191.961   $191.96   $191.95   $192.00  
  Purchase #7 $157.77   13.324%   $178.7913   $178.79   $178.80   $178.80  
  7 purchase totals = $971.22       $1,053.1270   $1,053.13   $1,053.10   $1,053.10