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 $212.53   11.182%   $236.2951   $236.30   $236.30   $236.30  
  Purchase #2 $52.99   3.355%   $54.7678   $54.77   $54.75   $54.80  
  Purchase #3 $85.64   11.765%   $95.7155   $95.72   $95.70   $95.70  
  Purchase #4 $147.85   4.701%   $154.8004   $154.80   $154.80   $154.80  
  Purchase #5 $126.96   5.681%   $134.1726   $134.17   $134.15   $134.20  
  Purchase #6 $117.65   8.662%   $127.8408   $127.84   $127.85   $127.80  
  Purchase #7 $112.99   3.403%   $116.835   $116.84   $116.85   $116.80  
  7 purchase totals = $856.61       $920.4272   $920.44   $920.40   $920.40