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 $185.42   8.856%   $201.8408   $201.84   $201.85   $201.80  
  Purchase #2 $56.95   8.771%   $61.9451   $61.95   $61.95   $61.90  
  Purchase #3 $109.73   8.275%   $118.8102   $118.81   $118.80   $118.80  
  Purchase #4 $122.37   6.834%   $130.7328   $130.73   $130.75   $130.70  
  Purchase #5 $210.78   6.147%   $223.7366   $223.74   $223.75   $223.70  
  Purchase #6 $139.25   10.595%   $154.0035   $154.00   $154.00   $154.00  
  Purchase #7 $33.25   5.114%   $34.9504   $34.95   $34.95   $35.00  
  7 purchase totals = $857.75       $926.0194   $926.02   $926.05   $925.90