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 $96.47   6.109%   $102.3634   $102.36   $102.35   $102.40  
  Purchase #2 $238.77   10.162%   $263.0338   $263.03   $263.05   $263.00  
  Purchase #3 $196.35   8.686%   $213.405   $213.41   $213.40   $213.40  
  Purchase #4 $55.32   3.543%   $57.28   $57.28   $57.30   $57.30  
  Purchase #5 $138.99   4.753%   $145.5962   $145.60   $145.60   $145.60  
  Purchase #6 $154.86   9.337%   $169.3193   $169.32   $169.30   $169.30  
  Purchase #7 $204.95   13.522%   $232.6633   $232.66   $232.65   $232.70  
  7 purchase totals = $1,085.71       $1,183.6610   $1,183.66   $1,183.65   $1,183.70