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 $151.94   7.703%   $163.6439   $163.64   $163.65   $163.60  
  Purchase #2 $96.64   9.746%   $106.0585   $106.06   $106.05   $106.10  
  Purchase #3 $219.26   11.823%   $245.1831   $245.18   $245.20   $245.20  
  Purchase #4 $83.75   12.870%   $94.5286   $94.53   $94.55   $94.50  
  Purchase #5 $159.41   10.646%   $176.3808   $176.38   $176.40   $176.40  
  Purchase #6 $122.41   5.861%   $129.5845   $129.58   $129.60   $129.60  
  Purchase #7 $101.99   5.131%   $107.2231   $107.22   $107.20   $107.20  
  7 purchase totals = $935.40       $1,022.6025   $1,022.59   $1,022.65   $1,022.60