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 $218.92   10.244%   $241.3462   $241.35   $241.35   $241.30  
  Purchase #2 $178.92   9.551%   $196.0086   $196.01   $196.00   $196.00  
  Purchase #3 $149.37   12.416%   $167.9158   $167.92   $167.90   $167.90  
  Purchase #4 $10.89   8.620%   $11.8287   $11.83   $11.85   $11.80  
  Purchase #5 $218.54   5.448%   $230.4461   $230.45   $230.45   $230.40  
  Purchase #6 $187.48   4.522%   $195.9578   $195.96   $195.95   $196.00  
  Purchase #7 $108.33   8.137%   $117.1448   $117.14   $117.15   $117.10  
  7 purchase totals = $1,072.45       $1,160.6480   $1,160.66   $1,160.65   $1,160.50