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 $33.88   6.267%   $36.0033   $36.00   $36.00   $36.00  
  Purchase #2 $134.92   13.665%   $153.3568   $153.36   $153.35   $153.40  
  Purchase #3 $227.59   11.497%   $253.756   $253.76   $253.75   $253.80  
  Purchase #4 $239.26   10.250%   $263.7842   $263.78   $263.80   $263.80  
  Purchase #5 $118.27   11.227%   $131.5482   $131.55   $131.55   $131.50  
  Purchase #6 $114.88   5.710%   $121.4396   $121.44   $121.45   $121.40  
  Purchase #7 $247.68   7.170%   $265.4387   $265.44   $265.45   $265.40  
  7 purchase totals = $1,116.48       $1,225.3268   $1,225.33   $1,225.35   $1,225.30