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 $98.66   3.469%   $102.0825   $102.08   $102.10   $102.10  
  Purchase #2 $86.73   12.443%   $97.5218   $97.52   $97.50   $97.50  
  Purchase #3 $22.62   7.708%   $24.3635   $24.36   $24.35   $24.40  
  Purchase #4 $124.37   9.769%   $136.5197   $136.52   $136.50   $136.50  
  Purchase #5 $239.54   12.703%   $269.9688   $269.97   $269.95   $270.00  
  Purchase #6 $95.97   4.412%   $100.2042   $100.20   $100.20   $100.20  
  Purchase #7 $24.69   5.401%   $26.0235   $26.02   $26.00   $26.00  
  7 purchase totals = $692.58       $756.6840   $756.67   $756.60   $756.70