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 $166.58   7.810%   $179.5899   $179.59   $179.60   $179.60  
  Purchase #2 $208.33   13.643%   $236.7525   $236.75   $236.75   $236.80  
  Purchase #3 $126.42   3.282%   $130.5691   $130.57   $130.55   $130.60  
  Purchase #4 $51.53   5.300%   $54.2611   $54.26   $54.25   $54.30  
  Purchase #5 $151.80   13.295%   $171.9818   $171.98   $172.00   $172.00  
  Purchase #6 $215.86   3.631%   $223.6979   $223.70   $223.70   $223.70  
  Purchase #7 $215.40   13.565%   $244.619   $244.62   $244.60   $244.60  
  7 purchase totals = $1,135.92       $1,241.4713   $1,241.47   $1,241.45   $1,241.60