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 $137.41   7.661%   $147.937   $147.94   $147.95   $147.90  
  Purchase #2 $82.34   3.143%   $84.9279   $84.93   $84.95   $84.90  
  Purchase #3 $191.99   5.709%   $202.9507   $202.95   $202.95   $203.00  
  Purchase #4 $214.85   11.636%   $239.8499   $239.85   $239.85   $239.80  
  Purchase #5 $140.56   4.732%   $147.2113   $147.21   $147.20   $147.20  
  Purchase #6 $36.97   12.429%   $41.565   $41.57   $41.55   $41.60  
  Purchase #7 $157.88   3.281%   $163.06   $163.06   $163.05   $163.10  
  7 purchase totals = $962.00       $1,027.5018   $1,027.51   $1,027.50   $1,027.50