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 $57.87   11.747%   $64.668   $64.67   $64.65   $64.70  
  Purchase #2 $124.55   10.496%   $137.6228   $137.62   $137.60   $137.60  
  Purchase #3 $202.28   4.865%   $212.1209   $212.12   $212.10   $212.10  
  Purchase #4 $230.88   8.151%   $249.699   $249.70   $249.70   $249.70  
  Purchase #5 $201.62   4.258%   $210.205   $210.21   $210.20   $210.20  
  Purchase #6 $168.42   13.632%   $191.379   $191.38   $191.40   $191.40  
  Purchase #7 $19.50   10.360%   $21.5202   $21.52   $21.50   $21.50  
  7 purchase totals = $1,005.12       $1,087.2149   $1,087.22   $1,087.15   $1,087.20