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 $60.69   7.766%   $65.4032   $65.40   $65.40   $65.40  
  Purchase #2 $56.70   9.691%   $62.1948   $62.19   $62.20   $62.20  
  Purchase #3 $147.34   12.595%   $165.8975   $165.90   $165.90   $165.90  
  Purchase #4 $193.58   11.217%   $215.2939   $215.29   $215.30   $215.30  
  Purchase #5 $248.46   9.792%   $272.7892   $272.79   $272.80   $272.80  
  Purchase #6 $63.48   4.649%   $66.4312   $66.43   $66.45   $66.40  
  Purchase #7 $141.30   4.265%   $147.3264   $147.33   $147.35   $147.30  
  7 purchase totals = $911.55       $995.3362   $995.33   $995.40   $995.30