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 $68.58   12.247%   $76.979   $76.98   $77.00   $77.00  
  Purchase #2 $30.40   4.274%   $31.6993   $31.70   $31.70   $31.70  
  Purchase #3 $112.82   7.726%   $121.5365   $121.54   $121.55   $121.50  
  Purchase #4 $128.33   3.131%   $132.348   $132.35   $132.35   $132.30  
  Purchase #5 $155.30   10.658%   $171.8519   $171.85   $171.85   $171.90  
  Purchase #6 $216.45   3.341%   $223.6816   $223.68   $223.70   $223.70  
  Purchase #7 $35.55   9.349%   $38.8736   $38.87   $38.85   $38.90  
  7 purchase totals = $747.43       $796.9699   $796.97   $797.00   $797.00