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 $86.35   7.558%   $92.8763   $92.88   $92.90   $92.90  
  Purchase #2 $249.64   5.490%   $263.3452   $263.35   $263.35   $263.30  
  Purchase #3 $98.51   4.198%   $102.6454   $102.65   $102.65   $102.60  
  Purchase #4 $135.40   5.872%   $143.3507   $143.35   $143.35   $143.40  
  Purchase #5 $71.45   3.471%   $73.93   $73.93   $73.95   $73.90  
  Purchase #6 $31.60   7.579%   $33.995   $34.00   $34.00   $34.00  
  Purchase #7 $27.83   8.608%   $30.2256   $30.23   $30.25   $30.20  
  7 purchase totals = $700.78       $740.3682   $740.39   $740.45   $740.30