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 $44.39   3.815%   $46.0835   $46.08   $46.10   $46.10  
  Purchase #2 $131.92   3.333%   $136.3169   $136.32   $136.30   $136.30  
  Purchase #3 $100.87   7.122%   $108.054   $108.05   $108.05   $108.10  
  Purchase #4 $173.46   13.715%   $197.25   $197.25   $197.25   $197.30  
  Purchase #5 $248.91   6.544%   $265.1987   $265.20   $265.20   $265.20  
  Purchase #6 $226.72   12.196%   $254.3708   $254.37   $254.35   $254.40  
  Purchase #7 $234.81   12.112%   $263.2502   $263.25   $263.25   $263.30  
  7 purchase totals = $1,161.08       $1,270.5241   $1,270.52   $1,270.50   $1,270.70