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 $229.25   8.258%   $248.1815   $248.18   $248.20   $248.20  
  Purchase #2 $107.34   9.494%   $117.5309   $117.53   $117.55   $117.50  
  Purchase #3 $220.65   10.717%   $244.2971   $244.30   $244.30   $244.30  
  Purchase #4 $222.76   9.769%   $244.5214   $244.52   $244.50   $244.50  
  Purchase #5 $191.38   5.411%   $201.7356   $201.74   $201.75   $201.70  
  Purchase #6 $63.58   7.391%   $68.2792   $68.28   $68.30   $68.30  
  Purchase #7 $76.35   13.525%   $86.6763   $86.68   $86.70   $86.70  
  7 purchase totals = $1,111.31       $1,211.2220   $1,211.23   $1,211.30   $1,211.20