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 $108.28   13.866%   $123.2941   $123.29   $123.30   $123.30  
  Purchase #2 $108.53   4.393%   $113.2977   $113.30   $113.30   $113.30  
  Purchase #3 $102.34   7.256%   $109.7658   $109.77   $109.75   $109.80  
  Purchase #4 $170.75   6.508%   $181.8624   $181.86   $181.85   $181.90  
  Purchase #5 $230.43   6.773%   $246.037   $246.04   $246.05   $246.00  
  Purchase #6 $72.44   12.634%   $81.5921   $81.59   $81.60   $81.60  
  Purchase #7 $163.68   4.301%   $170.7199   $170.72   $170.70   $170.70  
  7 purchase totals = $956.45       $1,026.5690   $1,026.57   $1,026.55   $1,026.60