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 $226.35   12.104%   $253.7474   $253.75   $253.75   $253.70  
  Purchase #2 $192.87   11.760%   $215.5515   $215.55   $215.55   $215.60  
  Purchase #3 $114.80   3.852%   $119.2221   $119.22   $119.20   $119.20  
  Purchase #4 $208.56   10.125%   $229.6767   $229.68   $229.70   $229.70  
  Purchase #5 $114.52   13.835%   $130.3638   $130.36   $130.35   $130.40  
  Purchase #6 $31.95   10.232%   $35.2191   $35.22   $35.20   $35.20  
  Purchase #7 $60.72   3.287%   $62.7159   $62.72   $62.70   $62.70  
  7 purchase totals = $949.77       $1,046.4965   $1,046.50   $1,046.45   $1,046.50