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 $222.94   5.734%   $235.7234   $235.72   $235.70   $235.70  
  Purchase #2 $43.89   13.591%   $49.8551   $49.86   $49.85   $49.90  
  Purchase #3 $23.52   7.130%   $25.197   $25.20   $25.20   $25.20  
  Purchase #4 $151.60   11.767%   $169.4388   $169.44   $169.45   $169.40  
  Purchase #5 $137.57   7.835%   $148.3486   $148.35   $148.35   $148.30  
  Purchase #6 $248.61   13.522%   $282.227   $282.23   $282.25   $282.20  
  Purchase #7 $193.59   13.428%   $219.5853   $219.59   $219.60   $219.60  
  7 purchase totals = $1,021.72       $1,130.3752   $1,130.39   $1,130.40   $1,130.30