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 $56.91   12.796%   $64.1922   $64.19   $64.20   $64.20  
  Purchase #2 $123.38   9.177%   $134.7026   $134.70   $134.70   $134.70  
  Purchase #3 $38.71   3.589%   $40.0993   $40.10   $40.10   $40.10  
  Purchase #4 $244.41   4.699%   $255.8948   $255.89   $255.90   $255.90  
  Purchase #5 $160.51   4.443%   $167.6415   $167.64   $167.65   $167.60  
  Purchase #6 $99.28   5.109%   $104.3522   $104.35   $104.35   $104.40  
  Purchase #7 $27.99   4.743%   $29.3176   $29.32   $29.30   $29.30  
  7 purchase totals = $751.19       $796.2002   $796.19   $796.20   $796.20