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 $47.65   4.826%   $49.9496   $49.95   $49.95   $49.90  
  Purchase #2 $136.61   13.610%   $155.2026   $155.20   $155.20   $155.20  
  Purchase #3 $55.47   3.254%   $57.275   $57.28   $57.30   $57.30  
  Purchase #4 $103.41   7.292%   $110.9507   $110.95   $110.95   $111.00  
  Purchase #5 $147.25   5.161%   $154.8496   $154.85   $154.85   $154.80  
  Purchase #6 $22.76   5.816%   $24.0837   $24.08   $24.10   $24.10  
  Purchase #7 $246.41   9.414%   $269.607   $269.61   $269.60   $269.60  
  7 purchase totals = $759.56       $821.9182   $821.92   $821.95   $821.90