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 $236.35   12.813%   $266.6335   $266.63   $266.65   $266.60  
  Purchase #2 $86.53   5.804%   $91.5522   $91.55   $91.55   $91.60  
  Purchase #3 $158.64   9.272%   $173.3491   $173.35   $173.35   $173.30  
  Purchase #4 $236.89   12.737%   $267.0627   $267.06   $267.05   $267.10  
  Purchase #5 $133.34   12.174%   $149.5728   $149.57   $149.55   $149.60  
  Purchase #6 $218.85   3.147%   $225.7372   $225.74   $225.75   $225.70  
  Purchase #7 $96.57   4.395%   $100.8143   $100.81   $100.80   $100.80  
  7 purchase totals = $1,167.17       $1,274.7218   $1,274.71   $1,274.70   $1,274.70