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 $231.66   13.618%   $263.2075   $263.21   $263.20   $263.20  
  Purchase #2 $213.52   10.445%   $235.8222   $235.82   $235.80   $235.80  
  Purchase #3 $91.40   8.192%   $98.8875   $98.89   $98.90   $98.90  
  Purchase #4 $153.75   3.123%   $158.5516   $158.55   $158.55   $158.60  
  Purchase #5 $247.83   13.765%   $281.9438   $281.94   $281.95   $281.90  
  Purchase #6 $185.35   5.235%   $195.0531   $195.05   $195.05   $195.10  
  Purchase #7 $241.90   4.586%   $252.9935   $252.99   $253.00   $253.00  
  7 purchase totals = $1,365.41       $1,486.4592   $1,486.45   $1,486.45   $1,486.50