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 $64.83   13.222%   $73.4018   $73.40   $73.40   $73.40  
  Purchase #2 $172.99   11.189%   $192.3459   $192.35   $192.35   $192.30  
  Purchase #3 $211.32   13.872%   $240.6343   $240.63   $240.65   $240.60  
  Purchase #4 $71.44   13.761%   $81.2709   $81.27   $81.25   $81.30  
  Purchase #5 $224.41   9.460%   $245.6392   $245.64   $245.65   $245.60  
  Purchase #6 $145.93   6.652%   $155.6373   $155.64   $155.65   $155.60  
  Purchase #7 $225.28   13.705%   $256.1546   $256.15   $256.15   $256.20  
  7 purchase totals = $1,116.20       $1,245.0840   $1,245.08   $1,245.10   $1,245.00