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 $111.93   10.773%   $123.9882   $123.99   $124.00   $124.00  
  Purchase #2 $101.87   6.824%   $108.8216   $108.82   $108.80   $108.80  
  Purchase #3 $85.99   8.501%   $93.3   $93.30   $93.30   $93.30  
  Purchase #4 $168.90   8.161%   $182.6839   $182.68   $182.70   $182.70  
  Purchase #5 $110.80   9.197%   $120.9903   $120.99   $121.00   $121.00  
  Purchase #6 $207.73   10.572%   $229.6912   $229.69   $229.70   $229.70  
  Purchase #7 $198.68   12.156%   $222.8315   $222.83   $222.85   $222.80  
  7 purchase totals = $985.90       $1,082.3067   $1,082.30   $1,082.35   $1,082.30