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 $222.96   11.532%   $248.6717   $248.67   $248.65   $248.70  
  Purchase #2 $152.71   8.157%   $165.1666   $165.17   $165.15   $165.20  
  Purchase #3 $156.32   7.737%   $168.4145   $168.41   $168.40   $168.40  
  Purchase #4 $88.68   11.617%   $98.982   $98.98   $99.00   $99.00  
  Purchase #5 $179.39   7.186%   $192.281   $192.28   $192.30   $192.30  
  Purchase #6 $67.41   12.576%   $75.8875   $75.89   $75.90   $75.90  
  Purchase #7 $64.75   13.156%   $73.2685   $73.27   $73.25   $73.30  
  7 purchase totals = $932.22       $1,022.6718   $1,022.67   $1,022.65   $1,022.80