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 $45.97   7.855%   $49.5809   $49.58   $49.60   $49.60  
  Purchase #2 $173.70   7.167%   $186.1491   $186.15   $186.15   $186.10  
  Purchase #3 $203.71   6.195%   $216.3298   $216.33   $216.35   $216.30  
  Purchase #4 $158.67   5.366%   $167.1842   $167.18   $167.20   $167.20  
  Purchase #5 $126.99   10.137%   $139.863   $139.86   $139.85   $139.90  
  Purchase #6 $246.65   4.415%   $257.5396   $257.54   $257.55   $257.50  
  Purchase #7 $15.81   9.655%   $17.3365   $17.34   $17.35   $17.30  
  7 purchase totals = $971.50       $1,033.9831   $1,033.98   $1,034.05   $1,033.90