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 $58.59   8.652%   $63.6592   $63.66   $63.65   $63.70  
  Purchase #2 $81.86   12.374%   $91.9894   $91.99   $92.00   $92.00  
  Purchase #3 $246.56   8.713%   $268.0428   $268.04   $268.05   $268.00  
  Purchase #4 $205.35   4.678%   $214.9563   $214.96   $214.95   $215.00  
  Purchase #5 $110.97   7.554%   $119.3527   $119.35   $119.35   $119.40  
  Purchase #6 $215.48   3.356%   $222.7115   $222.71   $222.70   $222.70  
  Purchase #7 $100.97   5.115%   $106.1346   $106.13   $106.15   $106.10  
  7 purchase totals = $1,019.78       $1,086.8465   $1,086.84   $1,086.85   $1,086.90