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 $246.32   8.384%   $266.9715   $266.97   $266.95   $267.00  
  Purchase #2 $27.48   8.329%   $29.7688   $29.77   $29.75   $29.80  
  Purchase #3 $79.81   7.702%   $85.957   $85.96   $85.95   $86.00  
  Purchase #4 $242.73   7.428%   $260.76   $260.76   $260.75   $260.80  
  Purchase #5 $71.86   9.637%   $78.7851   $78.79   $78.80   $78.80  
  Purchase #6 $218.64   7.852%   $235.8076   $235.81   $235.80   $235.80  
  Purchase #7 $166.76   6.856%   $178.1931   $178.19   $178.20   $178.20  
  7 purchase totals = $1,053.60       $1,136.2431   $1,136.25   $1,136.20   $1,136.40