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 $52.66   11.849%   $58.8997   $58.90   $58.90   $58.90  
  Purchase #2 $129.68   4.825%   $135.9371   $135.94   $135.95   $135.90  
  Purchase #3 $159.26   5.242%   $167.6084   $167.61   $167.60   $167.60  
  Purchase #4 $243.72   10.233%   $268.6599   $268.66   $268.65   $268.70  
  Purchase #5 $178.72   13.282%   $202.4576   $202.46   $202.45   $202.50  
  Purchase #6 $187.40   3.866%   $194.6449   $194.64   $194.65   $194.60  
  Purchase #7 $16.30   4.308%   $17.0022   $17.00   $17.00   $17.00  
  7 purchase totals = $967.74       $1,045.2098   $1,045.21   $1,045.20   $1,045.20