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 $207.83   13.451%   $235.7852   $235.79   $235.80   $235.80  
  Purchase #2 $130.42   12.422%   $146.6208   $146.62   $146.60   $146.60  
  Purchase #3 $91.34   6.104%   $96.9154   $96.92   $96.90   $96.90  
  Purchase #4 $243.26   12.352%   $273.3075   $273.31   $273.30   $273.30  
  Purchase #5 $131.94   4.555%   $137.9499   $137.95   $137.95   $137.90  
  Purchase #6 $47.90   11.607%   $53.4598   $53.46   $53.45   $53.50  
  Purchase #7 $240.30   9.178%   $262.3547   $262.35   $262.35   $262.40  
  7 purchase totals = $1,092.99       $1,206.3933   $1,206.40   $1,206.35   $1,206.40