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 $154.80   10.601%   $171.2103   $171.21   $171.20   $171.20  
  Purchase #2 $139.96   5.153%   $147.1721   $147.17   $147.15   $147.20  
  Purchase #3 $83.32   6.311%   $88.5783   $88.58   $88.60   $88.60  
  Purchase #4 $53.73   5.297%   $56.5761   $56.58   $56.60   $56.60  
  Purchase #5 $174.91   11.633%   $195.2573   $195.26   $195.25   $195.30  
  Purchase #6 $218.77   10.320%   $241.3471   $241.35   $241.35   $241.30  
  Purchase #7 $211.60   11.724%   $236.408   $236.41   $236.40   $236.40  
  7 purchase totals = $1,037.09       $1,136.5492   $1,136.56   $1,136.55   $1,136.60