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 $66.27   10.202%   $73.0309   $73.03   $73.05   $73.00  
  Purchase #2 $211.76   5.288%   $222.9579   $222.96   $222.95   $223.00  
  Purchase #3 $21.76   12.309%   $24.4384   $24.44   $24.45   $24.40  
  Purchase #4 $234.48   6.533%   $249.7986   $249.80   $249.80   $249.80  
  Purchase #5 $197.25   11.871%   $220.6655   $220.67   $220.65   $220.70  
  Purchase #6 $231.26   3.291%   $238.8708   $238.87   $238.85   $238.90  
  Purchase #7 $32.28   4.504%   $33.7339   $33.73   $33.75   $33.70  
  7 purchase totals = $995.06       $1,063.4960   $1,063.50   $1,063.50   $1,063.50