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 $158.81   3.126%   $163.7744   $163.77   $163.75   $163.80  
  Purchase #2 $231.28   12.623%   $260.4745   $260.47   $260.45   $260.50  
  Purchase #3 $88.50   8.693%   $96.1933   $96.19   $96.20   $96.20  
  Purchase #4 $163.38   9.265%   $178.5172   $178.52   $178.50   $178.50  
  Purchase #5 $245.72   6.710%   $262.2078   $262.21   $262.20   $262.20  
  Purchase #6 $132.45   5.553%   $139.8049   $139.80   $139.80   $139.80  
  Purchase #7 $249.70   10.374%   $275.6039   $275.60   $275.60   $275.60  
  7 purchase totals = $1,269.84       $1,376.5760   $1,376.56   $1,376.50   $1,376.60