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 $186.34   12.479%   $209.5934   $209.59   $209.60   $209.60  
  Purchase #2 $92.76   13.593%   $105.3689   $105.37   $105.35   $105.40  
  Purchase #3 $165.79   8.138%   $179.282   $179.28   $179.30   $179.30  
  Purchase #4 $60.83   3.330%   $62.8556   $62.86   $62.85   $62.90  
  Purchase #5 $176.96   13.811%   $201.3999   $201.40   $201.40   $201.40  
  Purchase #6 $112.58   5.304%   $118.5512   $118.55   $118.55   $118.60  
  Purchase #7 $202.80   9.359%   $221.7801   $221.78   $221.80   $221.80  
  7 purchase totals = $998.06       $1,098.8311   $1,098.83   $1,098.85   $1,099.00