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 $95.95   8.354%   $103.9657   $103.97   $103.95   $104.00  
  Purchase #2 $230.48   10.326%   $254.2794   $254.28   $254.30   $254.30  
  Purchase #3 $183.97   12.495%   $206.9571   $206.96   $206.95   $207.00  
  Purchase #4 $45.71   5.110%   $48.0458   $48.05   $48.05   $48.00  
  Purchase #5 $233.73   4.301%   $243.7827   $243.78   $243.80   $243.80  
  Purchase #6 $113.73   6.334%   $120.9337   $120.93   $120.95   $120.90  
  Purchase #7 $57.47   7.145%   $61.5762   $61.58   $61.60   $61.60  
  7 purchase totals = $961.04       $1,039.5406   $1,039.55   $1,039.60   $1,039.60