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 $113.68   7.615%   $122.3367   $122.34   $122.35   $122.30  
  Purchase #2 $103.65   12.346%   $116.4466   $116.45   $116.45   $116.40  
  Purchase #3 $202.69   5.268%   $213.3677   $213.37   $213.35   $213.40  
  Purchase #4 $16.61   4.338%   $17.3305   $17.33   $17.35   $17.30  
  Purchase #5 $229.38   10.862%   $254.2953   $254.30   $254.30   $254.30  
  Purchase #6 $221.58   12.253%   $248.7302   $248.73   $248.75   $248.70  
  Purchase #7 $84.52   10.424%   $93.3304   $93.33   $93.35   $93.30  
  7 purchase totals = $972.11       $1,065.8374   $1,065.85   $1,065.90   $1,065.70