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 $163.41   12.793%   $184.315   $184.32   $184.30   $184.30  
  Purchase #2 $50.66   13.591%   $57.5452   $57.55   $57.55   $57.50  
  Purchase #3 $116.81   5.762%   $123.5406   $123.54   $123.55   $123.50  
  Purchase #4 $248.56   9.728%   $272.7399   $272.74   $272.75   $272.70  
  Purchase #5 $36.45   7.717%   $39.2628   $39.26   $39.25   $39.30  
  Purchase #6 $201.47   11.341%   $224.3187   $224.32   $224.30   $224.30  
  Purchase #7 $202.83   6.446%   $215.9044   $215.90   $215.90   $215.90  
  7 purchase totals = $1,020.19       $1,117.6266   $1,117.63   $1,117.60   $1,117.50