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 $70.64   3.555%   $73.1513   $73.15   $73.15   $73.20  
  Purchase #2 $151.87   8.488%   $164.7607   $164.76   $164.75   $164.80  
  Purchase #3 $112.67   5.644%   $119.0291   $119.03   $119.05   $119.00  
  Purchase #4 $71.30   8.614%   $77.4418   $77.44   $77.45   $77.40  
  Purchase #5 $179.37   12.547%   $201.8756   $201.88   $201.90   $201.90  
  Purchase #6 $210.57   9.453%   $230.4752   $230.48   $230.50   $230.50  
  Purchase #7 $84.54   3.725%   $87.6891   $87.69   $87.70   $87.70  
  7 purchase totals = $880.96       $954.4228   $954.43   $954.50   $954.50