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 $70.29   5.565%   $74.2016   $74.20   $74.20   $74.20  
  Purchase #2 $245.55   9.624%   $269.1817   $269.18   $269.20   $269.20  
  Purchase #3 $230.94   13.741%   $262.6735   $262.67   $262.65   $262.70  
  Purchase #4 $165.47   7.238%   $177.4467   $177.45   $177.45   $177.40  
  Purchase #5 $112.37   13.236%   $127.2433   $127.24   $127.25   $127.20  
  Purchase #6 $30.74   4.616%   $32.159   $32.16   $32.15   $32.20  
  Purchase #7 $179.75   12.104%   $201.5069   $201.51   $201.50   $201.50  
  7 purchase totals = $1,035.11       $1,144.4127   $1,144.41   $1,144.40   $1,144.40