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 $63.60   7.108%   $68.1207   $68.12   $68.10   $68.10  
  Purchase #2 $233.96   12.213%   $262.5335   $262.53   $262.55   $262.50  
  Purchase #3 $178.71   3.404%   $184.7933   $184.79   $184.80   $184.80  
  Purchase #4 $136.69   5.589%   $144.3296   $144.33   $144.35   $144.30  
  Purchase #5 $218.95   8.203%   $236.9105   $236.91   $236.90   $236.90  
  Purchase #6 $155.84   13.170%   $176.3641   $176.36   $176.35   $176.40  
  Purchase #7 $237.70   6.732%   $253.702   $253.70   $253.70   $253.70  
  7 purchase totals = $1,225.45       $1,326.7537   $1,326.74   $1,326.75   $1,326.70