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 $48.61   8.228%   $52.6096   $52.61   $52.60   $52.60  
  Purchase #2 $141.97   10.626%   $157.0557   $157.06   $157.05   $157.10  
  Purchase #3 $122.68   9.610%   $134.4695   $134.47   $134.45   $134.50  
  Purchase #4 $163.84   4.842%   $171.7731   $171.77   $171.75   $171.80  
  Purchase #5 $238.47   3.393%   $246.5613   $246.56   $246.55   $246.60  
  Purchase #6 $112.95   13.614%   $128.327   $128.33   $128.35   $128.30  
  Purchase #7 $102.81   13.235%   $116.4169   $116.42   $116.40   $116.40  
  7 purchase totals = $931.33       $1,007.2131   $1,007.22   $1,007.15   $1,007.30