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 $209.93   5.521%   $221.5202   $221.52   $221.50   $221.50  
  Purchase #2 $159.46   12.473%   $179.3494   $179.35   $179.35   $179.30  
  Purchase #3 $228.37   4.392%   $238.4   $238.40   $238.40   $238.40  
  Purchase #4 $220.44   8.606%   $239.4111   $239.41   $239.40   $239.40  
  Purchase #5 $119.57   12.370%   $134.3608   $134.36   $134.35   $134.40  
  Purchase #6 $153.90   10.194%   $169.5886   $169.59   $169.60   $169.60  
  Purchase #7 $232.74   8.397%   $252.2832   $252.28   $252.30   $252.30  
  7 purchase totals = $1,324.41       $1,434.9133   $1,434.91   $1,434.90   $1,434.90