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 $119.52   4.596%   $125.0131   $125.01   $125.00   $125.00  
  Purchase #2 $228.92   11.824%   $255.9875   $255.99   $256.00   $256.00  
  Purchase #3 $123.99   13.384%   $140.5848   $140.58   $140.60   $140.60  
  Purchase #4 $119.86   9.292%   $130.9974   $131.00   $131.00   $131.00  
  Purchase #5 $155.42   13.483%   $176.3753   $176.38   $176.40   $176.40  
  Purchase #6 $115.37   6.110%   $122.4191   $122.42   $122.40   $122.40  
  Purchase #7 $16.80   11.604%   $18.7495   $18.75   $18.75   $18.70  
  7 purchase totals = $879.88       $970.1267   $970.13   $970.15   $970.10