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 $163.60   8.307%   $177.1903   $177.19   $177.20   $177.20  
  Purchase #2 $98.59   13.240%   $111.6433   $111.64   $111.65   $111.60  
  Purchase #3 $234.66   7.341%   $251.8864   $251.89   $251.90   $251.90  
  Purchase #4 $155.35   3.393%   $160.621   $160.62   $160.60   $160.60  
  Purchase #5 $102.74   11.644%   $114.703   $114.70   $114.70   $114.70  
  Purchase #6 $200.91   13.752%   $228.5391   $228.54   $228.55   $228.50  
  Purchase #7 $22.47   12.576%   $25.2958   $25.30   $25.30   $25.30  
  7 purchase totals = $978.32       $1,069.8789   $1,069.88   $1,069.90   $1,069.80