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 $64.65   5.840%   $68.4256   $68.43   $68.45   $68.40  
  Purchase #2 $51.54   4.368%   $53.7913   $53.79   $53.80   $53.80  
  Purchase #3 $70.48   5.744%   $74.5284   $74.53   $74.55   $74.50  
  Purchase #4 $112.26   5.595%   $118.5409   $118.54   $118.55   $118.50  
  Purchase #5 $33.95   9.827%   $37.2863   $37.29   $37.30   $37.30  
  Purchase #6 $107.79   5.498%   $113.7163   $113.72   $113.70   $113.70  
  Purchase #7 $134.37   3.452%   $139.0085   $139.01   $139.00   $139.00  
  7 purchase totals = $575.04       $605.2973   $605.31   $605.35   $605.20