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 $82.67   4.686%   $86.5439   $86.54   $86.55   $86.50  
  Purchase #2 $133.98   3.713%   $138.9547   $138.95   $138.95   $139.00  
  Purchase #3 $162.57   3.854%   $168.8354   $168.84   $168.85   $168.80  
  Purchase #4 $125.39   9.855%   $137.7472   $137.75   $137.75   $137.70  
  Purchase #5 $204.89   4.242%   $213.5814   $213.58   $213.60   $213.60  
  Purchase #6 $226.77   4.127%   $236.1288   $236.13   $236.15   $236.10  
  Purchase #7 $56.93   5.418%   $60.0145   $60.01   $60.00   $60.00  
  7 purchase totals = $993.20       $1,041.8059   $1,041.80   $1,041.85   $1,041.70