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 $156.53   9.852%   $171.9513   $171.95   $171.95   $172.00  
  Purchase #2 $154.67   10.123%   $170.3272   $170.33   $170.35   $170.30  
  Purchase #3 $210.81   10.401%   $232.7363   $232.74   $232.75   $232.70  
  Purchase #4 $119.29   4.448%   $124.596   $124.60   $124.60   $124.60  
  Purchase #5 $130.32   7.412%   $139.9793   $139.98   $140.00   $140.00  
  Purchase #6 $15.57   9.351%   $17.026   $17.03   $17.05   $17.00  
  Purchase #7 $157.46   4.636%   $164.7598   $164.76   $164.75   $164.80  
  7 purchase totals = $944.65       $1,021.3759   $1,021.39   $1,021.45   $1,021.40