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 $71.54   6.208%   $75.9812   $75.98   $76.00   $76.00  
  Purchase #2 $130.99   12.248%   $147.0337   $147.03   $147.05   $147.00  
  Purchase #3 $161.33   9.640%   $176.8822   $176.88   $176.90   $176.90  
  Purchase #4 $58.43   6.444%   $62.1952   $62.20   $62.20   $62.20  
  Purchase #5 $65.33   10.120%   $71.9414   $71.94   $71.95   $71.90  
  Purchase #6 $17.45   10.291%   $19.2458   $19.25   $19.25   $19.20  
  Purchase #7 $196.35   10.197%   $216.3718   $216.37   $216.35   $216.40  
  7 purchase totals = $701.42       $769.6513   $769.65   $769.70   $769.60