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 $226.71   11.623%   $253.0605   $253.06   $253.05   $253.10  
  Purchase #2 $53.91   12.597%   $60.701   $60.70   $60.70   $60.70  
  Purchase #3 $226.95   9.433%   $248.3582   $248.36   $248.35   $248.40  
  Purchase #4 $248.38   13.197%   $281.1587   $281.16   $281.15   $281.20  
  Purchase #5 $198.96   8.455%   $215.7821   $215.78   $215.80   $215.80  
  Purchase #6 $63.93   11.454%   $71.2525   $71.25   $71.25   $71.30  
  Purchase #7 $21.89   10.597%   $24.2097   $24.21   $24.20   $24.20  
  7 purchase totals = $1,040.73       $1,154.5227   $1,154.52   $1,154.50   $1,154.70