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 $224.54   12.336%   $252.2393   $252.24   $252.25   $252.20  
  Purchase #2 $233.44   3.824%   $242.3667   $242.37   $242.35   $242.40  
  Purchase #3 $73.77   5.646%   $77.9351   $77.94   $77.95   $77.90  
  Purchase #4 $132.29   11.461%   $147.4518   $147.45   $147.45   $147.50  
  Purchase #5 $230.85   9.131%   $251.9289   $251.93   $251.95   $251.90  
  Purchase #6 $243.87   4.437%   $254.6905   $254.69   $254.70   $254.70  
  Purchase #7 $56.76   5.734%   $60.0146   $60.01   $60.00   $60.00  
  7 purchase totals = $1,195.52       $1,286.6269   $1,286.63   $1,286.65   $1,286.60