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 $240.94   4.772%   $252.4377   $252.44   $252.45   $252.40  
  Purchase #2 $239.33   13.510%   $271.6635   $271.66   $271.65   $271.70  
  Purchase #3 $209.69   4.488%   $219.1009   $219.10   $219.10   $219.10  
  Purchase #4 $174.55   13.274%   $197.7198   $197.72   $197.70   $197.70  
  Purchase #5 $211.34   10.474%   $233.4758   $233.48   $233.50   $233.50  
  Purchase #6 $89.83   9.276%   $98.1626   $98.16   $98.15   $98.20  
  Purchase #7 $170.97   11.157%   $190.0451   $190.05   $190.05   $190.00  
  7 purchase totals = $1,336.65       $1,462.6054   $1,462.61   $1,462.60   $1,462.60