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 $184.42   11.643%   $205.892   $205.89   $205.90   $205.90  
  Purchase #2 $59.52   7.511%   $63.9905   $63.99   $64.00   $64.00  
  Purchase #3 $97.51   11.393%   $108.6193   $108.62   $108.60   $108.60  
  Purchase #4 $156.84   10.629%   $173.5105   $173.51   $173.50   $173.50  
  Purchase #5 $52.39   5.634%   $55.3417   $55.34   $55.35   $55.30  
  Purchase #6 $236.67   5.868%   $250.5578   $250.56   $250.55   $250.60  
  Purchase #7 $182.89   5.193%   $192.3875   $192.39   $192.40   $192.40  
  7 purchase totals = $970.24       $1,050.2993   $1,050.30   $1,050.30   $1,050.30