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 $39.84   9.558%   $43.6479   $43.65   $43.65   $43.60  
  Purchase #2 $111.70   5.754%   $118.1272   $118.13   $118.15   $118.10  
  Purchase #3 $196.56   5.133%   $206.6494   $206.65   $206.65   $206.60  
  Purchase #4 $164.96   8.716%   $179.3379   $179.34   $179.35   $179.30  
  Purchase #5 $15.93   8.501%   $17.2842   $17.28   $17.30   $17.30  
  Purchase #6 $153.54   9.793%   $168.5762   $168.58   $168.60   $168.60  
  Purchase #7 $218.37   3.716%   $226.4846   $226.48   $226.50   $226.50  
  7 purchase totals = $900.90       $960.1074   $960.11   $960.20   $960.00