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 $109.97   12.151%   $123.3325   $123.33   $123.35   $123.30  
  Purchase #2 $223.75   13.121%   $253.1082   $253.11   $253.10   $253.10  
  Purchase #3 $21.28   6.527%   $22.6689   $22.67   $22.65   $22.70  
  Purchase #4 $151.33   7.632%   $162.8795   $162.88   $162.90   $162.90  
  Purchase #5 $176.91   3.211%   $182.5906   $182.59   $182.60   $182.60  
  Purchase #6 $58.94   9.720%   $64.669   $64.67   $64.65   $64.70  
  Purchase #7 $177.57   13.336%   $201.2507   $201.25   $201.25   $201.30  
  7 purchase totals = $919.75       $1,010.4994   $1,010.50   $1,010.50   $1,010.60