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 $52.41   13.583%   $59.5289   $59.53   $59.55   $59.50  
  Purchase #2 $121.52   10.293%   $134.0281   $134.03   $134.05   $134.00  
  Purchase #3 $57.45   10.845%   $63.6805   $63.68   $63.70   $63.70  
  Purchase #4 $197.36   6.572%   $210.3305   $210.33   $210.35   $210.30  
  Purchase #5 $174.95   6.787%   $186.8239   $186.82   $186.80   $186.80  
  Purchase #6 $52.88   9.205%   $57.7476   $57.75   $57.75   $57.70  
  Purchase #7 $227.69   11.525%   $253.9313   $253.93   $253.95   $253.90  
  7 purchase totals = $884.26       $966.0708   $966.07   $966.15   $965.90