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 $206.68   5.543%   $218.1363   $218.14   $218.15   $218.10  
  Purchase #2 $228.42   12.702%   $257.4339   $257.43   $257.45   $257.40  
  Purchase #3 $88.49   5.650%   $93.4897   $93.49   $93.50   $93.50  
  Purchase #4 $102.83   8.854%   $111.9346   $111.93   $111.95   $111.90  
  Purchase #5 $220.99   5.723%   $233.6373   $233.64   $233.65   $233.60  
  Purchase #6 $189.54   12.596%   $213.4145   $213.41   $213.40   $213.40  
  Purchase #7 $195.79   10.742%   $216.8218   $216.82   $216.80   $216.80  
  7 purchase totals = $1,232.74       $1,344.8681   $1,344.86   $1,344.90   $1,344.70