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 $94.58   10.551%   $104.5591   $104.56   $104.55   $104.60  
  Purchase #2 $64.32   12.854%   $72.5877   $72.59   $72.60   $72.60  
  Purchase #3 $46.75   11.350%   $52.0561   $52.06   $52.05   $52.10  
  Purchase #4 $146.97   4.279%   $153.2588   $153.26   $153.25   $153.30  
  Purchase #5 $119.80   6.339%   $127.3941   $127.39   $127.40   $127.40  
  Purchase #6 $198.77   13.864%   $226.3275   $226.33   $226.35   $226.30  
  Purchase #7 $6.51   7.799%   $7.0177   $7.02   $7.00   $7.00  
  7 purchase totals = $677.70       $743.2010   $743.21   $743.20   $743.30