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 $249.61   7.734%   $268.9148   $268.91   $268.90   $268.90  
  Purchase #2 $128.89   9.664%   $141.3459   $141.35   $141.35   $141.30  
  Purchase #3 $23.53   5.679%   $24.8663   $24.87   $24.85   $24.90  
  Purchase #4 $61.44   3.114%   $63.3532   $63.35   $63.35   $63.40  
  Purchase #5 $141.74   5.678%   $149.788   $149.79   $149.80   $149.80  
  Purchase #6 $246.90   8.445%   $267.7507   $267.75   $267.75   $267.80  
  Purchase #7 $118.59   12.715%   $133.6687   $133.67   $133.65   $133.70  
  7 purchase totals = $970.70       $1,049.6876   $1,049.69   $1,049.65   $1,049.80