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 $208.82   12.436%   $234.7889   $234.79   $234.80   $234.80  
  Purchase #2 $102.67   10.570%   $113.5222   $113.52   $113.50   $113.50  
  Purchase #3 $44.33   4.702%   $46.4144   $46.41   $46.40   $46.40  
  Purchase #4 $66.95   7.522%   $71.986   $71.99   $72.00   $72.00  
  Purchase #5 $161.87   9.583%   $177.382   $177.38   $177.40   $177.40  
  Purchase #6 $54.52   5.155%   $57.3305   $57.33   $57.35   $57.30  
  Purchase #7 $66.72   10.843%   $73.9544   $73.95   $73.95   $74.00  
  7 purchase totals = $705.88       $775.3784   $775.37   $775.40   $775.40