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 $186.62   11.730%   $208.5105   $208.51   $208.50   $208.50  
  Purchase #2 $209.65   12.356%   $235.5544   $235.55   $235.55   $235.60  
  Purchase #3 $60.43   4.188%   $62.9608   $62.96   $62.95   $63.00  
  Purchase #4 $41.33   6.647%   $44.0772   $44.08   $44.10   $44.10  
  Purchase #5 $237.64   8.785%   $258.5167   $258.52   $258.50   $258.50  
  Purchase #6 $112.52   10.866%   $124.7464   $124.75   $124.75   $124.70  
  Purchase #7 $81.25   4.169%   $84.6373   $84.64   $84.65   $84.60  
  7 purchase totals = $929.44       $1,019.0033   $1,019.01   $1,019.00   $1,019.00