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 $37.50   10.581%   $41.4679   $41.47   $41.45   $41.50  
  Purchase #2 $233.31   8.124%   $252.2641   $252.26   $252.25   $252.30  
  Purchase #3 $117.92   13.807%   $134.2012   $134.20   $134.20   $134.20  
  Purchase #4 $66.25   7.725%   $71.3678   $71.37   $71.35   $71.40  
  Purchase #5 $218.90   6.854%   $233.9034   $233.90   $233.90   $233.90  
  Purchase #6 $56.73   4.637%   $59.3606   $59.36   $59.35   $59.40  
  Purchase #7 $54.51   10.589%   $60.2821   $60.28   $60.30   $60.30  
  7 purchase totals = $785.12       $852.8471   $852.84   $852.80   $853.00