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 $145.96   5.623%   $154.1673   $154.17   $154.15   $154.20  
  Purchase #2 $153.39   3.616%   $158.9366   $158.94   $158.95   $158.90  
  Purchase #3 $244.81   7.142%   $262.2943   $262.29   $262.30   $262.30  
  Purchase #4 $184.59   13.418%   $209.3583   $209.36   $209.35   $209.40  
  Purchase #5 $224.38   3.240%   $231.6499   $231.65   $231.65   $231.60  
  Purchase #6 $192.96   6.864%   $206.2048   $206.20   $206.20   $206.20  
  Purchase #7 $20.67   13.643%   $23.49   $23.49   $23.50   $23.50  
  7 purchase totals = $1,166.76       $1,246.1012   $1,246.10   $1,246.10   $1,246.10