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 $230.55   4.169%   $240.1616   $240.16   $240.15   $240.20  
  Purchase #2 $50.80   5.343%   $53.5142   $53.51   $53.50   $53.50  
  Purchase #3 $70.71   13.246%   $80.0762   $80.08   $80.10   $80.10  
  Purchase #4 $140.50   9.854%   $154.3449   $154.34   $154.35   $154.30  
  Purchase #5 $245.89   12.262%   $276.041   $276.04   $276.05   $276.00  
  Purchase #6 $177.40   3.561%   $183.7172   $183.72   $183.70   $183.70  
  Purchase #7 $245.59   7.726%   $264.5643   $264.56   $264.55   $264.60  
  7 purchase totals = $1,161.44       $1,252.4194   $1,252.41   $1,252.40   $1,252.40