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 $202.57   11.657%   $226.1836   $226.18   $226.20   $226.20  
  Purchase #2 $141.31   13.630%   $160.5706   $160.57   $160.55   $160.60  
  Purchase #3 $67.83   12.317%   $76.1846   $76.18   $76.20   $76.20  
  Purchase #4 $77.87   8.414%   $84.422   $84.42   $84.40   $84.40  
  Purchase #5 $245.62   13.285%   $278.2506   $278.25   $278.25   $278.30  
  Purchase #6 $41.95   10.412%   $46.3178   $46.32   $46.30   $46.30  
  Purchase #7 $23.42   5.809%   $24.7805   $24.78   $24.80   $24.80  
  7 purchase totals = $800.57       $896.7097   $896.70   $896.70   $896.80