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 $182.71   12.364%   $205.3003   $205.30   $205.30   $205.30  
  Purchase #2 $199.75   4.296%   $208.3313   $208.33   $208.35   $208.30  
  Purchase #3 $170.91   11.752%   $190.9953   $191.00   $191.00   $191.00  
  Purchase #4 $207.65   4.397%   $216.7804   $216.78   $216.80   $216.80  
  Purchase #5 $16.44   12.452%   $18.4871   $18.49   $18.50   $18.50  
  Purchase #6 $194.62   12.794%   $219.5197   $219.52   $219.50   $219.50  
  Purchase #7 $152.96   6.697%   $163.2037   $163.20   $163.20   $163.20  
  7 purchase totals = $1,125.04       $1,222.6178   $1,222.62   $1,222.65   $1,222.60