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 $138.47   10.459%   $152.9526   $152.95   $152.95   $153.00  
  Purchase #2 $190.74   8.734%   $207.3992   $207.40   $207.40   $207.40  
  Purchase #3 $158.36   8.556%   $171.9093   $171.91   $171.90   $171.90  
  Purchase #4 $218.99   8.409%   $237.4049   $237.40   $237.40   $237.40  
  Purchase #5 $246.94   8.370%   $267.6089   $267.61   $267.60   $267.60  
  Purchase #6 $110.72   13.689%   $125.8765   $125.88   $125.90   $125.90  
  Purchase #7 $11.74   12.430%   $13.1993   $13.20   $13.20   $13.20  
  7 purchase totals = $1,075.96       $1,176.3507   $1,176.35   $1,176.35   $1,176.40