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 $73.66   11.804%   $82.3548   $82.35   $82.35   $82.40  
  Purchase #2 $249.67   10.774%   $276.5694   $276.57   $276.55   $276.60  
  Purchase #3 $152.27   9.245%   $166.3474   $166.35   $166.35   $166.30  
  Purchase #4 $16.56   4.349%   $17.2802   $17.28   $17.30   $17.30  
  Purchase #5 $225.37   10.323%   $248.6349   $248.63   $248.65   $248.60  
  Purchase #6 $56.79   11.431%   $63.2817   $63.28   $63.30   $63.30  
  Purchase #7 $196.77   6.306%   $209.1783   $209.18   $209.20   $209.20  
  7 purchase totals = $971.09       $1,063.6467   $1,063.64   $1,063.70   $1,063.70