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 $57.25   6.544%   $60.9964   $61.00   $61.00   $61.00  
  Purchase #2 $115.99   12.531%   $130.5247   $130.52   $130.50   $130.50  
  Purchase #3 $93.90   4.167%   $97.8128   $97.81   $97.80   $97.80  
  Purchase #4 $196.81   3.464%   $203.6275   $203.63   $203.65   $203.60  
  Purchase #5 $89.84   7.198%   $96.3067   $96.31   $96.30   $96.30  
  Purchase #6 $24.40   6.664%   $26.026   $26.03   $26.05   $26.00  
  Purchase #7 $113.51   3.249%   $117.1979   $117.20   $117.20   $117.20  
  7 purchase totals = $691.70       $732.4920   $732.50   $732.50   $732.40