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 $234.60   13.106%   $265.3467   $265.35   $265.35   $265.30  
  Purchase #2 $59.54   9.491%   $65.1909   $65.19   $65.20   $65.20  
  Purchase #3 $191.34   6.146%   $203.0998   $203.10   $203.10   $203.10  
  Purchase #4 $67.79   3.276%   $70.0108   $70.01   $70.00   $70.00  
  Purchase #5 $48.78   8.778%   $53.0619   $53.06   $53.05   $53.10  
  Purchase #6 $208.61   7.516%   $224.2891   $224.29   $224.30   $224.30  
  Purchase #7 $164.99   5.774%   $174.5165   $174.52   $174.50   $174.50  
  7 purchase totals = $975.65       $1,055.5157   $1,055.52   $1,055.50   $1,055.50