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 $63.51   7.593%   $68.3323   $68.33   $68.35   $68.30  
  Purchase #2 $179.71   10.592%   $198.7449   $198.74   $198.75   $198.70  
  Purchase #3 $92.81   5.831%   $98.2218   $98.22   $98.20   $98.20  
  Purchase #4 $195.59   11.784%   $218.6383   $218.64   $218.65   $218.60  
  Purchase #5 $58.46   12.356%   $65.6833   $65.68   $65.70   $65.70  
  Purchase #6 $119.41   12.501%   $134.3374   $134.34   $134.35   $134.30  
  Purchase #7 $241.81   9.708%   $265.2849   $265.28   $265.30   $265.30  
  7 purchase totals = $951.30       $1,049.2429   $1,049.23   $1,049.30   $1,049.10