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 $226.63   11.626%   $252.978   $252.98   $253.00   $253.00  
  Purchase #2 $8.54   3.858%   $8.8695   $8.87   $8.85   $8.90  
  Purchase #3 $112.71   5.286%   $118.6679   $118.67   $118.65   $118.70  
  Purchase #4 $134.77   8.198%   $145.8184   $145.82   $145.80   $145.80  
  Purchase #5 $241.32   5.262%   $254.0183   $254.02   $254.00   $254.00  
  Purchase #6 $231.82   11.658%   $258.8456   $258.85   $258.85   $258.80  
  Purchase #7 $14.67   7.631%   $15.7895   $15.79   $15.80   $15.80  
  7 purchase totals = $970.46       $1,054.9872   $1,055.00   $1,054.95   $1,055.00