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 $215.49   4.760%   $225.7473   $225.75   $225.75   $225.70  
  Purchase #2 $9.73   10.729%   $10.7739   $10.77   $10.75   $10.80  
  Purchase #3 $85.99   8.482%   $93.2837   $93.28   $93.30   $93.30  
  Purchase #4 $235.97   5.451%   $248.8327   $248.83   $248.85   $248.80  
  Purchase #5 $96.82   6.585%   $103.1956   $103.20   $103.20   $103.20  
  Purchase #6 $22.29   4.224%   $23.2315   $23.23   $23.25   $23.20  
  Purchase #7 $17.43   4.807%   $18.2679   $18.27   $18.25   $18.30  
  7 purchase totals = $683.72       $723.3326   $723.33   $723.35   $723.30