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 $37.86   9.824%   $41.5794   $41.58   $41.60   $41.60  
  Purchase #2 $243.32   6.598%   $259.3743   $259.37   $259.35   $259.40  
  Purchase #3 $32.89   5.118%   $34.5733   $34.57   $34.55   $34.60  
  Purchase #4 $40.40   10.582%   $44.6751   $44.68   $44.70   $44.70  
  Purchase #5 $229.41   3.135%   $236.602   $236.60   $236.60   $236.60  
  Purchase #6 $184.97   4.749%   $193.7542   $193.75   $193.75   $193.80  
  Purchase #7 $147.59   10.460%   $163.0279   $163.03   $163.05   $163.00  
  7 purchase totals = $916.44       $973.5862   $973.58   $973.60   $973.70