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 $46.91   10.853%   $52.0011   $52.00   $52.00   $52.00  
  Purchase #2 $122.44   3.113%   $126.2516   $126.25   $126.25   $126.30  
  Purchase #3 $26.64   7.152%   $28.5453   $28.55   $28.55   $28.50  
  Purchase #4 $36.84   8.349%   $39.9158   $39.92   $39.90   $39.90  
  Purchase #5 $168.98   5.520%   $178.3077   $178.31   $178.30   $178.30  
  Purchase #6 $119.88   11.417%   $133.5667   $133.57   $133.55   $133.60  
  Purchase #7 $153.93   11.509%   $171.6458   $171.65   $171.65   $171.60  
  7 purchase totals = $675.62       $730.2340   $730.25   $730.20   $730.20