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 $52.94   6.392%   $56.3239   $56.32   $56.30   $56.30  
  Purchase #2 $183.29   9.515%   $200.73   $200.73   $200.75   $200.70  
  Purchase #3 $61.66   9.131%   $67.2902   $67.29   $67.30   $67.30  
  Purchase #4 $214.80   12.429%   $241.4975   $241.50   $241.50   $241.50  
  Purchase #5 $121.64   10.378%   $134.2638   $134.26   $134.25   $134.30  
  Purchase #6 $208.32   12.384%   $234.1183   $234.12   $234.10   $234.10  
  Purchase #7 $84.31   5.279%   $88.7607   $88.76   $88.75   $88.80  
  7 purchase totals = $926.96       $1,022.9844   $1,022.98   $1,022.95   $1,023.00