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 $187.35   11.444%   $208.7903   $208.79   $208.80   $208.80  
  Purchase #2 $151.52   5.831%   $160.3551   $160.36   $160.35   $160.40  
  Purchase #3 $80.95   7.381%   $86.9249   $86.92   $86.90   $86.90  
  Purchase #4 $118.54   3.262%   $122.4068   $122.41   $122.40   $122.40  
  Purchase #5 $224.27   7.590%   $241.2921   $241.29   $241.30   $241.30  
  Purchase #6 $56.48   3.796%   $58.624   $58.62   $58.60   $58.60  
  Purchase #7 $123.73   5.701%   $130.7838   $130.78   $130.80   $130.80  
  7 purchase totals = $942.84       $1,009.1770   $1,009.17   $1,009.15   $1,009.20