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 $237.91   10.532%   $262.9667   $262.97   $262.95   $263.00  
  Purchase #2 $157.89   5.874%   $167.1645   $167.16   $167.15   $167.20  
  Purchase #3 $135.75   12.414%   $152.602   $152.60   $152.60   $152.60  
  Purchase #4 $86.43   10.834%   $95.7938   $95.79   $95.80   $95.80  
  Purchase #5 $65.44   7.436%   $70.3061   $70.31   $70.30   $70.30  
  Purchase #6 $87.73   6.699%   $93.607   $93.61   $93.60   $93.60  
  Purchase #7 $45.77   4.673%   $47.9088   $47.91   $47.90   $47.90  
  7 purchase totals = $816.92       $890.3489   $890.35   $890.30   $890.40