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 $154.29   13.821%   $175.6144   $175.61   $175.60   $175.60  
  Purchase #2 $188.97   8.671%   $205.3556   $205.36   $205.35   $205.40  
  Purchase #3 $189.96   12.212%   $213.1579   $213.16   $213.15   $213.20  
  Purchase #4 $26.86   3.286%   $27.7426   $27.74   $27.75   $27.70  
  Purchase #5 $192.66   5.506%   $203.2679   $203.27   $203.25   $203.30  
  Purchase #6 $124.32   7.451%   $133.5831   $133.58   $133.60   $133.60  
  Purchase #7 $205.64   13.546%   $233.496   $233.50   $233.50   $233.50  
  7 purchase totals = $1,082.70       $1,192.2175   $1,192.22   $1,192.20   $1,192.30