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 $160.49   13.525%   $182.1963   $182.20   $182.20   $182.20  
  Purchase #2 $134.33   6.339%   $142.8452   $142.85   $142.85   $142.80  
  Purchase #3 $28.46   4.426%   $29.7196   $29.72   $29.70   $29.70  
  Purchase #4 $141.98   11.630%   $158.4923   $158.49   $158.50   $158.50  
  Purchase #5 $92.46   3.297%   $95.5084   $95.51   $95.50   $95.50  
  Purchase #6 $197.54   3.789%   $205.0248   $205.02   $205.00   $205.00  
  Purchase #7 $231.65   6.150%   $245.8965   $245.90   $245.90   $245.90  
  7 purchase totals = $986.91       $1,059.6831   $1,059.69   $1,059.65   $1,059.60