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 $92.68   6.423%   $98.6328   $98.63   $98.65   $98.60  
  Purchase #2 $164.65   12.145%   $184.6467   $184.65   $184.65   $184.60  
  Purchase #3 $133.46   4.134%   $138.9772   $138.98   $139.00   $139.00  
  Purchase #4 $221.80   3.191%   $228.8776   $228.88   $228.90   $228.90  
  Purchase #5 $90.43   3.605%   $93.69   $93.69   $93.70   $93.70  
  Purchase #6 $229.81   6.253%   $244.18   $244.18   $244.20   $244.20  
  Purchase #7 $174.38   4.176%   $181.6621   $181.66   $181.65   $181.70  
  7 purchase totals = $1,107.21       $1,170.6664   $1,170.67   $1,170.75   $1,170.70