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 $166.41   12.362%   $186.9816   $186.98   $187.00   $187.00  
  Purchase #2 $80.37   6.241%   $85.3859   $85.39   $85.40   $85.40  
  Purchase #3 $69.49   13.787%   $79.0706   $79.07   $79.05   $79.10  
  Purchase #4 $178.44   8.682%   $193.9322   $193.93   $193.95   $193.90  
  Purchase #5 $225.81   13.470%   $256.2266   $256.23   $256.25   $256.20  
  Purchase #6 $44.96   5.478%   $47.4229   $47.42   $47.40   $47.40  
  Purchase #7 $151.99   8.826%   $165.4046   $165.40   $165.40   $165.40  
  7 purchase totals = $917.47       $1,014.4244   $1,014.42   $1,014.45   $1,014.40