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 $9.54   4.533%   $9.9724   $9.97   $9.95   $10.00  
  Purchase #2 $230.41   3.171%   $237.7163   $237.72   $237.70   $237.70  
  Purchase #3 $19.88   10.166%   $21.901   $21.90   $21.90   $21.90  
  Purchase #4 $21.31   8.130%   $23.0425   $23.04   $23.05   $23.00  
  Purchase #5 $235.25   3.548%   $243.5967   $243.60   $243.60   $243.60  
  Purchase #6 $33.52   3.731%   $34.7706   $34.77   $34.75   $34.80  
  Purchase #7 $7.61   4.855%   $7.9795   $7.98   $8.00   $8.00  
  7 purchase totals = $557.52       $578.9790   $578.98   $578.95   $579.00