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 $58.58   12.127%   $65.684   $65.68   $65.70   $65.70  
  Purchase #2 $155.31   13.433%   $176.1728   $176.17   $176.15   $176.20  
  Purchase #3 $234.64   4.187%   $244.4644   $244.46   $244.45   $244.50  
  Purchase #4 $103.49   5.839%   $109.5328   $109.53   $109.55   $109.50  
  Purchase #5 $191.81   3.286%   $198.1129   $198.11   $198.10   $198.10  
  Purchase #6 $16.39   12.793%   $18.4868   $18.49   $18.50   $18.50  
  Purchase #7 $195.35   4.279%   $203.709   $203.71   $203.70   $203.70  
  7 purchase totals = $955.57       $1,016.1627   $1,016.15   $1,016.15   $1,016.20