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 $135.83   12.221%   $152.4298   $152.43   $152.45   $152.40  
  Purchase #2 $243.32   9.860%   $267.3114   $267.31   $267.30   $267.30  
  Purchase #3 $33.37   9.757%   $36.6259   $36.63   $36.65   $36.60  
  Purchase #4 $127.73   5.606%   $134.8905   $134.89   $134.90   $134.90  
  Purchase #5 $180.57   6.595%   $192.4786   $192.48   $192.50   $192.50  
  Purchase #6 $145.88   12.718%   $164.433   $164.43   $164.45   $164.40  
  Purchase #7 $83.49   12.111%   $93.6015   $93.60   $93.60   $93.60  
  7 purchase totals = $950.19       $1,041.7707   $1,041.77   $1,041.85   $1,041.70