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 $85.31   8.627%   $92.6697   $92.67   $92.65   $92.70  
  Purchase #2 $206.78   5.755%   $218.6802   $218.68   $218.70   $218.70  
  Purchase #3 $121.42   7.300%   $130.2837   $130.28   $130.30   $130.30  
  Purchase #4 $110.89   5.679%   $117.1874   $117.19   $117.20   $117.20  
  Purchase #5 $250.55   4.633%   $262.158   $262.16   $262.15   $262.20  
  Purchase #6 $115.55   12.451%   $129.9371   $129.94   $129.95   $129.90  
  Purchase #7 $19.57   12.469%   $22.0102   $22.01   $22.00   $22.00  
  7 purchase totals = $910.07       $972.9263   $972.93   $972.95   $973.00