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 $54.42   10.621%   $60.1999   $60.20   $60.20   $60.20  
  Purchase #2 $150.64   8.183%   $162.9669   $162.97   $162.95   $163.00  
  Purchase #3 $59.69   4.463%   $62.354   $62.35   $62.35   $62.40  
  Purchase #4 $203.86   9.333%   $222.8863   $222.89   $222.90   $222.90  
  Purchase #5 $248.41   9.598%   $272.2524   $272.25   $272.25   $272.30  
  Purchase #6 $137.46   5.229%   $144.6478   $144.65   $144.65   $144.60  
  Purchase #7 $107.47   11.856%   $120.2116   $120.21   $120.20   $120.20  
  7 purchase totals = $961.95       $1,045.5189   $1,045.52   $1,045.50   $1,045.60