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 $22.37   11.814%   $25.0128   $25.01   $25.00   $25.00  
  Purchase #2 $145.89   5.769%   $154.3064   $154.31   $154.30   $154.30  
  Purchase #3 $5.62   6.256%   $5.9716   $5.97   $5.95   $6.00  
  Purchase #4 $223.60   12.208%   $250.8971   $250.90   $250.90   $250.90  
  Purchase #5 $127.97   12.548%   $144.0277   $144.03   $144.05   $144.00  
  Purchase #6 $190.33   5.348%   $200.5088   $200.51   $200.50   $200.50  
  Purchase #7 $153.59   13.401%   $174.1726   $174.17   $174.15   $174.20  
  7 purchase totals = $869.37       $954.8970   $954.90   $954.85   $954.90