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 $68.32   12.577%   $76.9126   $76.91   $76.90   $76.90  
  Purchase #2 $49.98   4.833%   $52.3955   $52.40   $52.40   $52.40  
  Purchase #3 $194.69   10.458%   $215.0507   $215.05   $215.05   $215.10  
  Purchase #4 $89.70   7.740%   $96.6428   $96.64   $96.65   $96.60  
  Purchase #5 $187.98   9.600%   $206.0261   $206.03   $206.05   $206.00  
  Purchase #6 $224.67   5.415%   $236.8359   $236.84   $236.85   $236.80  
  Purchase #7 $112.71   9.535%   $123.4569   $123.46   $123.45   $123.50  
  7 purchase totals = $928.05       $1,007.3205   $1,007.33   $1,007.35   $1,007.30