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 $76.58   12.708%   $86.3118   $86.31   $86.30   $86.30  
  Purchase #2 $231.60   4.192%   $241.3087   $241.31   $241.30   $241.30  
  Purchase #3 $142.68   3.662%   $147.9049   $147.90   $147.90   $147.90  
  Purchase #4 $149.59   8.646%   $162.5236   $162.52   $162.50   $162.50  
  Purchase #5 $82.74   12.311%   $92.9261   $92.93   $92.95   $92.90  
  Purchase #6 $214.34   5.112%   $225.2971   $225.30   $225.30   $225.30  
  Purchase #7 $76.64   13.422%   $86.9266   $86.93   $86.95   $86.90  
  7 purchase totals = $974.17       $1,043.1988   $1,043.20   $1,043.20   $1,043.10