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 $58.43   4.705%   $61.1791   $61.18   $61.20   $61.20  
  Purchase #2 $119.87   8.668%   $130.2603   $130.26   $130.25   $130.30  
  Purchase #3 $47.32   12.797%   $53.3755   $53.38   $53.40   $53.40  
  Purchase #4 $222.96   3.645%   $231.0869   $231.09   $231.10   $231.10  
  Purchase #5 $212.77   12.543%   $239.4577   $239.46   $239.45   $239.50  
  Purchase #6 $125.49   5.186%   $131.9979   $132.00   $132.00   $132.00  
  Purchase #7 $158.79   4.303%   $165.6227   $165.62   $165.60   $165.60  
  7 purchase totals = $945.63       $1,012.9801   $1,012.99   $1,013.00   $1,013.10