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 $156.53   3.548%   $162.0837   $162.08   $162.10   $162.10  
  Purchase #2 $239.96   6.153%   $254.7247   $254.72   $254.70   $254.70  
  Purchase #3 $143.25   10.503%   $158.2955   $158.30   $158.30   $158.30  
  Purchase #4 $235.73   9.205%   $257.4289   $257.43   $257.45   $257.40  
  Purchase #5 $52.54   5.234%   $55.2899   $55.29   $55.30   $55.30  
  Purchase #6 $200.61   3.111%   $206.851   $206.85   $206.85   $206.90  
  Purchase #7 $123.65   5.397%   $130.3234   $130.32   $130.30   $130.30  
  7 purchase totals = $1,152.27       $1,224.9971   $1,224.99   $1,225.00   $1,225.00