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 $58.62   11.470%   $65.3437   $65.34   $65.35   $65.30  
  Purchase #2 $167.87   11.710%   $187.5276   $187.53   $187.55   $187.50  
  Purchase #3 $73.40   9.364%   $80.2732   $80.27   $80.25   $80.30  
  Purchase #4 $139.85   5.359%   $147.3446   $147.34   $147.35   $147.30  
  Purchase #5 $29.30   3.737%   $30.3949   $30.39   $30.40   $30.40  
  Purchase #6 $58.40   11.205%   $64.9437   $64.94   $64.95   $64.90  
  Purchase #7 $217.29   11.158%   $241.5352   $241.54   $241.55   $241.50  
  7 purchase totals = $744.73       $817.3629   $817.35   $817.40   $817.20