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 $201.25   3.642%   $208.5795   $208.58   $208.60   $208.60  
  Purchase #2 $117.96   4.694%   $123.497   $123.50   $123.50   $123.50  
  Purchase #3 $41.27   6.250%   $43.8494   $43.85   $43.85   $43.80  
  Purchase #4 $15.33   13.216%   $17.356   $17.36   $17.35   $17.40  
  Purchase #5 $98.87   8.717%   $107.4885   $107.49   $107.50   $107.50  
  Purchase #6 $244.95   6.117%   $259.9336   $259.93   $259.95   $259.90  
  Purchase #7 $242.52   3.818%   $251.7794   $251.78   $251.80   $251.80  
  7 purchase totals = $962.15       $1,012.4834   $1,012.49   $1,012.55   $1,012.50