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 $184.69   10.652%   $204.3632   $204.36   $204.35   $204.40  
  Purchase #2 $197.41   11.399%   $219.9128   $219.91   $219.90   $219.90  
  Purchase #3 $211.37   9.252%   $230.926   $230.93   $230.95   $230.90  
  Purchase #4 $185.85   9.719%   $203.9128   $203.91   $203.90   $203.90  
  Purchase #5 $22.25   9.688%   $24.4056   $24.41   $24.40   $24.40  
  Purchase #6 $8.62   3.266%   $8.9015   $8.90   $8.90   $8.90  
  Purchase #7 $89.54   5.702%   $94.6456   $94.65   $94.65   $94.60  
  7 purchase totals = $899.73       $987.0675   $987.07   $987.05   $987.00