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 $214.64   6.186%   $227.9176   $227.92   $227.90   $227.90  
  Purchase #2 $243.27   11.794%   $271.9613   $271.96   $271.95   $272.00  
  Purchase #3 $243.37   9.531%   $266.5656   $266.57   $266.55   $266.60  
  Purchase #4 $195.54   5.280%   $205.8645   $205.86   $205.85   $205.90  
  Purchase #5 $72.83   12.168%   $81.692   $81.69   $81.70   $81.70  
  Purchase #6 $145.43   7.104%   $155.7613   $155.76   $155.75   $155.80  
  Purchase #7 $131.88   9.837%   $144.853   $144.85   $144.85   $144.90  
  7 purchase totals = $1,246.96       $1,354.6153   $1,354.61   $1,354.55   $1,354.80