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 $192.52   9.604%   $211.0096   $211.01   $211.00   $211.00  
  Purchase #2 $83.85   10.373%   $92.5478   $92.55   $92.55   $92.50  
  Purchase #3 $225.46   10.338%   $248.7681   $248.77   $248.75   $248.80  
  Purchase #4 $230.88   3.521%   $239.0093   $239.01   $239.00   $239.00  
  Purchase #5 $185.27   13.328%   $209.9628   $209.96   $209.95   $210.00  
  Purchase #6 $241.61   10.816%   $267.7425   $267.74   $267.75   $267.70  
  Purchase #7 $23.59   13.738%   $26.8308   $26.83   $26.85   $26.80  
  7 purchase totals = $1,183.18       $1,295.8709   $1,295.87   $1,295.85   $1,295.80