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 $161.70   10.679%   $178.9679   $178.97   $178.95   $179.00  
  Purchase #2 $30.43   13.868%   $34.65   $34.65   $34.65   $34.70  
  Purchase #3 $233.79   8.520%   $253.7089   $253.71   $253.70   $253.70  
  Purchase #4 $189.95   9.153%   $207.3361   $207.34   $207.35   $207.30  
  Purchase #5 $55.36   12.830%   $62.4627   $62.46   $62.45   $62.50  
  Purchase #6 $101.35   13.337%   $114.867   $114.87   $114.85   $114.90  
  Purchase #7 $211.91   9.538%   $232.122   $232.12   $232.10   $232.10  
  7 purchase totals = $984.49       $1,084.1146   $1,084.12   $1,084.05   $1,084.20