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 $158.77   11.647%   $177.2619   $177.26   $177.25   $177.30  
  Purchase #2 $200.25   7.199%   $214.666   $214.67   $214.65   $214.70  
  Purchase #3 $237.82   10.832%   $263.5807   $263.58   $263.60   $263.60  
  Purchase #4 $72.92   12.293%   $81.8841   $81.88   $81.90   $81.90  
  Purchase #5 $100.82   3.390%   $104.2378   $104.24   $104.25   $104.20  
  Purchase #6 $152.60   6.200%   $162.0612   $162.06   $162.05   $162.10  
  Purchase #7 $44.74   3.303%   $46.2178   $46.22   $46.20   $46.20  
  7 purchase totals = $967.92       $1,049.9095   $1,049.91   $1,049.90   $1,050.00