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 $216.27   13.570%   $245.6178   $245.62   $245.60   $245.60  
  Purchase #2 $162.27   9.593%   $177.8366   $177.84   $177.85   $177.80  
  Purchase #3 $59.28   3.850%   $61.5623   $61.56   $61.55   $61.60  
  Purchase #4 $136.85   3.571%   $141.7369   $141.74   $141.75   $141.70  
  Purchase #5 $210.53   11.770%   $235.3094   $235.31   $235.30   $235.30  
  Purchase #6 $163.54   10.215%   $180.2456   $180.25   $180.25   $180.20  
  Purchase #7 $208.70   4.867%   $218.8574   $218.86   $218.85   $218.90  
  7 purchase totals = $1,157.44       $1,261.1660   $1,261.18   $1,261.15   $1,261.10