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 $38.56   8.196%   $41.7204   $41.72   $41.70   $41.70  
  Purchase #2 $59.46   4.770%   $62.2962   $62.30   $62.30   $62.30  
  Purchase #3 $212.55   6.632%   $226.6463   $226.65   $226.65   $226.60  
  Purchase #4 $90.83   5.357%   $95.6958   $95.70   $95.70   $95.70  
  Purchase #5 $83.40   9.217%   $91.087   $91.09   $91.10   $91.10  
  Purchase #6 $6.69   8.811%   $7.2795   $7.28   $7.30   $7.30  
  Purchase #7 $149.47   3.155%   $154.1858   $154.19   $154.20   $154.20  
  7 purchase totals = $640.96       $678.9110   $678.93   $678.95   $678.90