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 $41.49   5.345%   $43.7076   $43.71   $43.70   $43.70  
  Purchase #2 $172.60   12.167%   $193.6002   $193.60   $193.60   $193.60  
  Purchase #3 $18.95   11.143%   $21.0616   $21.06   $21.05   $21.10  
  Purchase #4 $129.56   8.813%   $140.9781   $140.98   $141.00   $141.00  
  Purchase #5 $182.71   4.820%   $191.5166   $191.52   $191.50   $191.50  
  Purchase #6 $159.89   5.197%   $168.1995   $168.20   $168.20   $168.20  
  Purchase #7 $198.26   4.675%   $207.5287   $207.53   $207.55   $207.50  
  7 purchase totals = $903.46       $966.5923   $966.60   $966.60   $966.60