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 $53.50   11.574%   $59.6921   $59.69   $59.70   $59.70  
  Purchase #2 $34.93   8.759%   $37.9895   $37.99   $38.00   $38.00  
  Purchase #3 $216.52   10.828%   $239.9648   $239.96   $239.95   $240.00  
  Purchase #4 $19.33   3.738%   $20.0526   $20.05   $20.05   $20.10  
  Purchase #5 $242.66   11.416%   $270.3621   $270.36   $270.35   $270.40  
  Purchase #6 $153.89   6.376%   $163.702   $163.70   $163.70   $163.70  
  Purchase #7 $239.68   11.441%   $267.1018   $267.10   $267.10   $267.10  
  7 purchase totals = $960.51       $1,058.8649   $1,058.85   $1,058.85   $1,059.00