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 $55.43   9.138%   $60.4952   $60.50   $60.50   $60.50  
  Purchase #2 $243.29   8.355%   $263.6169   $263.62   $263.60   $263.60  
  Purchase #3 $167.33   11.363%   $186.3437   $186.34   $186.35   $186.30  
  Purchase #4 $239.45   8.785%   $260.4857   $260.49   $260.50   $260.50  
  Purchase #5 $200.92   5.451%   $211.8721   $211.87   $211.85   $211.90  
  Purchase #6 $179.68   12.119%   $201.4554   $201.46   $201.45   $201.50  
  Purchase #7 $214.52   4.378%   $223.9117   $223.91   $223.90   $223.90  
  7 purchase totals = $1,300.62       $1,408.1807   $1,408.19   $1,408.15   $1,408.20