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 $236.32   13.389%   $267.9609   $267.96   $267.95   $268.00  
  Purchase #2 $184.69   5.564%   $194.9662   $194.97   $194.95   $195.00  
  Purchase #3 $49.87   4.747%   $52.2373   $52.24   $52.25   $52.20  
  Purchase #4 $120.37   13.292%   $136.3696   $136.37   $136.35   $136.40  
  Purchase #5 $65.42   5.471%   $68.9991   $69.00   $69.00   $69.00  
  Purchase #6 $182.75   9.777%   $200.6175   $200.62   $200.60   $200.60  
  Purchase #7 $211.41   3.401%   $218.6001   $218.60   $218.60   $218.60  
  7 purchase totals = $1,050.83       $1,139.7507   $1,139.76   $1,139.70   $1,139.80