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 $109.95   13.685%   $124.9967   $125.00   $125.00   $125.00  
  Purchase #2 $50.32   6.426%   $53.5536   $53.55   $53.55   $53.60  
  Purchase #3 $146.88   7.158%   $157.3937   $157.39   $157.40   $157.40  
  Purchase #4 $202.51   9.603%   $221.957   $221.96   $221.95   $222.00  
  Purchase #5 $209.52   12.852%   $236.4475   $236.45   $236.45   $236.40  
  Purchase #6 $107.41   13.390%   $121.7922   $121.79   $121.80   $121.80  
  Purchase #7 $132.49   5.323%   $139.5424   $139.54   $139.55   $139.50  
  7 purchase totals = $959.08       $1,055.6831   $1,055.68   $1,055.70   $1,055.70