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 $211.31   6.413%   $224.8613   $224.86   $224.85   $224.90  
  Purchase #2 $35.39   5.253%   $37.249   $37.25   $37.25   $37.20  
  Purchase #3 $114.72   9.207%   $125.2823   $125.28   $125.30   $125.30  
  Purchase #4 $53.93   5.474%   $56.8821   $56.88   $56.90   $56.90  
  Purchase #5 $215.76   6.482%   $229.7456   $229.75   $229.75   $229.70  
  Purchase #6 $84.69   12.452%   $95.2356   $95.24   $95.25   $95.20  
  Purchase #7 $233.79   7.809%   $252.0467   $252.05   $252.05   $252.00  
  7 purchase totals = $949.59       $1,021.3026   $1,021.31   $1,021.35   $1,021.20