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 $106.85   10.695%   $118.2776   $118.28   $118.30   $118.30  
  Purchase #2 $244.99   12.114%   $274.6681   $274.67   $274.65   $274.70  
  Purchase #3 $73.97   3.740%   $76.7365   $76.74   $76.75   $76.70  
  Purchase #4 $204.71   6.508%   $218.0325   $218.03   $218.05   $218.00  
  Purchase #5 $47.84   12.808%   $53.9673   $53.97   $53.95   $54.00  
  Purchase #6 $178.38   3.577%   $184.7607   $184.76   $184.75   $184.80  
  Purchase #7 $223.65   4.192%   $233.0254   $233.03   $233.05   $233.00  
  7 purchase totals = $1,080.39       $1,159.4681   $1,159.48   $1,159.50   $1,159.50