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 $30.55   6.568%   $32.5565   $32.56   $32.55   $32.60  
  Purchase #2 $239.74   5.498%   $252.9209   $252.92   $252.90   $252.90  
  Purchase #3 $183.76   4.738%   $192.4665   $192.47   $192.45   $192.50  
  Purchase #4 $218.50   8.704%   $237.5182   $237.52   $237.50   $237.50  
  Purchase #5 $59.61   7.287%   $63.9538   $63.95   $63.95   $64.00  
  Purchase #6 $79.89   4.314%   $83.3365   $83.34   $83.35   $83.30  
  Purchase #7 $164.90   6.232%   $175.1766   $175.18   $175.20   $175.20  
  7 purchase totals = $976.95       $1,037.9290   $1,037.94   $1,037.90   $1,038.00