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 $169.82   10.418%   $187.5118   $187.51   $187.50   $187.50  
  Purchase #2 $185.86   12.860%   $209.7616   $209.76   $209.75   $209.80  
  Purchase #3 $23.72   3.337%   $24.5115   $24.51   $24.50   $24.50  
  Purchase #4 $241.57   10.289%   $266.4251   $266.43   $266.45   $266.40  
  Purchase #5 $63.29   12.206%   $71.0152   $71.02   $71.00   $71.00  
  Purchase #6 $248.54   12.391%   $279.3366   $279.34   $279.35   $279.30  
  Purchase #7 $234.54   6.670%   $250.1838   $250.18   $250.20   $250.20  
  7 purchase totals = $1,167.34       $1,288.7456   $1,288.75   $1,288.75   $1,288.70