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 $48.29   10.282%   $53.2552   $53.26   $53.25   $53.30  
  Purchase #2 $215.72   7.693%   $232.3153   $232.32   $232.30   $232.30  
  Purchase #3 $77.64   3.720%   $80.5282   $80.53   $80.55   $80.50  
  Purchase #4 $203.88   11.342%   $227.0041   $227.00   $227.00   $227.00  
  Purchase #5 $63.36   7.303%   $67.9872   $67.99   $68.00   $68.00  
  Purchase #6 $19.42   11.458%   $21.6451   $21.65   $21.65   $21.60  
  Purchase #7 $162.63   11.155%   $180.7714   $180.77   $180.75   $180.80  
  7 purchase totals = $790.94       $863.5065   $863.52   $863.50   $863.50