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 $189.52   9.178%   $206.9141   $206.91   $206.90   $206.90  
  Purchase #2 $185.79   8.697%   $201.9482   $201.95   $201.95   $201.90  
  Purchase #3 $152.60   12.152%   $171.144   $171.14   $171.15   $171.10  
  Purchase #4 $49.87   7.228%   $53.4746   $53.47   $53.45   $53.50  
  Purchase #5 $157.97   13.681%   $179.5819   $179.58   $179.60   $179.60  
  Purchase #6 $33.68   9.191%   $36.7755   $36.78   $36.80   $36.80  
  Purchase #7 $250.92   13.504%   $284.8042   $284.80   $284.80   $284.80  
  7 purchase totals = $1,020.35       $1,134.6425   $1,134.63   $1,134.65   $1,134.60