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 $64.52   13.611%   $73.3018   $73.30   $73.30   $73.30  
  Purchase #2 $80.99   7.116%   $86.7532   $86.75   $86.75   $86.80  
  Purchase #3 $12.55   4.442%   $13.1075   $13.11   $13.10   $13.10  
  Purchase #4 $146.37   11.797%   $163.6373   $163.64   $163.65   $163.60  
  Purchase #5 $240.79   7.580%   $259.0419   $259.04   $259.05   $259.00  
  Purchase #6 $126.27   13.804%   $143.7003   $143.70   $143.70   $143.70  
  Purchase #7 $214.39   10.850%   $237.6513   $237.65   $237.65   $237.70  
  7 purchase totals = $885.88       $977.1933   $977.19   $977.20   $977.20