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 $58.98   10.298%   $65.0538   $65.05   $65.05   $65.10  
  Purchase #2 $178.53   12.406%   $200.6784   $200.68   $200.70   $200.70  
  Purchase #3 $201.93   13.572%   $229.3359   $229.34   $229.35   $229.30  
  Purchase #4 $65.65   5.659%   $69.3651   $69.37   $69.35   $69.40  
  Purchase #5 $141.66   7.470%   $152.242   $152.24   $152.25   $152.20  
  Purchase #6 $229.86   11.664%   $256.6709   $256.67   $256.65   $256.70  
  Purchase #7 $245.93   7.314%   $263.9173   $263.92   $263.90   $263.90  
  7 purchase totals = $1,122.54       $1,237.2634   $1,237.27   $1,237.25   $1,237.30