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 $183.97   12.838%   $207.5881   $207.59   $207.60   $207.60  
  Purchase #2 $203.93   10.174%   $224.6778   $224.68   $224.70   $224.70  
  Purchase #3 $47.72   3.386%   $49.3358   $49.34   $49.35   $49.30  
  Purchase #4 $117.46   10.515%   $129.8109   $129.81   $129.80   $129.80  
  Purchase #5 $247.84   7.155%   $265.573   $265.57   $265.55   $265.60  
  Purchase #6 $205.72   6.741%   $219.5876   $219.59   $219.60   $219.60  
  Purchase #7 $69.66   5.247%   $73.3151   $73.32   $73.30   $73.30  
  7 purchase totals = $1,076.30       $1,169.8883   $1,169.90   $1,169.90   $1,169.90