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 $223.97   11.573%   $249.89   $249.89   $249.90   $249.90  
  Purchase #2 $97.87   8.778%   $106.461   $106.46   $106.45   $106.50  
  Purchase #3 $115.82   10.509%   $127.9915   $127.99   $128.00   $128.00  
  Purchase #4 $86.67   8.354%   $93.9104   $93.91   $93.90   $93.90  
  Purchase #5 $124.84   10.696%   $138.1929   $138.19   $138.20   $138.20  
  Purchase #6 $224.79   11.846%   $251.4186   $251.42   $251.40   $251.40  
  Purchase #7 $46.53   12.295%   $52.2509   $52.25   $52.25   $52.30  
  7 purchase totals = $920.49       $1,020.1153   $1,020.11   $1,020.10   $1,020.20