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 $77.32   11.174%   $85.9597   $85.96   $85.95   $86.00  
  Purchase #2 $117.42   13.379%   $133.1296   $133.13   $133.15   $133.10  
  Purchase #3 $44.56   7.265%   $47.7973   $47.80   $47.80   $47.80  
  Purchase #4 $222.70   6.686%   $237.5897   $237.59   $237.60   $237.60  
  Purchase #5 $30.79   4.700%   $32.2371   $32.24   $32.25   $32.20  
  Purchase #6 $157.89   9.233%   $172.468   $172.47   $172.45   $172.50  
  Purchase #7 $205.50   3.546%   $212.787   $212.79   $212.80   $212.80  
  7 purchase totals = $856.18       $921.9684   $921.98   $922.00   $922.00