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 $58.77   13.827%   $66.8961   $66.90   $66.90   $66.90  
  Purchase #2 $101.52   4.732%   $106.3239   $106.32   $106.30   $106.30  
  Purchase #3 $179.63   8.169%   $194.304   $194.30   $194.30   $194.30  
  Purchase #4 $155.92   6.454%   $165.9831   $165.98   $166.00   $166.00  
  Purchase #5 $75.44   7.610%   $81.181   $81.18   $81.20   $81.20  
  Purchase #6 $53.41   12.353%   $60.0077   $60.01   $60.00   $60.00  
  Purchase #7 $163.69   13.408%   $185.6376   $185.64   $185.65   $185.60  
  7 purchase totals = $788.38       $860.3334   $860.33   $860.35   $860.30