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 $49.85   13.862%   $56.7602   $56.76   $56.75   $56.80  
  Purchase #2 $159.92   12.373%   $179.7069   $179.71   $179.70   $179.70  
  Purchase #3 $86.88   11.515%   $96.8842   $96.88   $96.90   $96.90  
  Purchase #4 $222.61   4.254%   $232.0798   $232.08   $232.10   $232.10  
  Purchase #5 $27.56   7.227%   $29.5518   $29.55   $29.55   $29.60  
  Purchase #6 $45.40   12.155%   $50.9184   $50.92   $50.90   $50.90  
  Purchase #7 $108.36   7.552%   $116.5433   $116.54   $116.55   $116.50  
  7 purchase totals = $700.58       $762.4446   $762.44   $762.45   $762.50