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 $248.29   7.146%   $266.0328   $266.03   $266.05   $266.00  
  Purchase #2 $86.70   10.873%   $96.1269   $96.13   $96.15   $96.10  
  Purchase #3 $159.64   11.317%   $177.7065   $177.71   $177.70   $177.70  
  Purchase #4 $23.34   6.169%   $24.7798   $24.78   $24.80   $24.80  
  Purchase #5 $212.97   9.169%   $232.4972   $232.50   $232.50   $232.50  
  Purchase #6 $106.90   9.501%   $117.0566   $117.06   $117.05   $117.10  
  Purchase #7 $214.77   3.795%   $222.9205   $222.92   $222.90   $222.90  
  7 purchase totals = $1,052.61       $1,137.1203   $1,137.13   $1,137.15   $1,137.10