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 $58.62   9.497%   $64.1871   $64.19   $64.20   $64.20  
  Purchase #2 $113.80   10.624%   $125.8901   $125.89   $125.90   $125.90  
  Purchase #3 $66.82   4.312%   $69.7013   $69.70   $69.70   $69.70  
  Purchase #4 $211.59   11.490%   $235.9017   $235.90   $235.90   $235.90  
  Purchase #5 $160.44   4.487%   $167.6389   $167.64   $167.65   $167.60  
  Purchase #6 $142.87   11.301%   $159.0157   $159.02   $159.00   $159.00  
  Purchase #7 $34.49   11.114%   $38.3232   $38.32   $38.30   $38.30  
  7 purchase totals = $788.63       $860.6580   $860.66   $860.65   $860.60