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 $191.53   13.305%   $217.0131   $217.01   $217.00   $217.00  
  Purchase #2 $207.92   8.379%   $225.3416   $225.34   $225.35   $225.30  
  Purchase #3 $23.98   5.769%   $25.3634   $25.36   $25.35   $25.40  
  Purchase #4 $247.29   7.239%   $265.1913   $265.19   $265.20   $265.20  
  Purchase #5 $111.98   13.786%   $127.4176   $127.42   $127.40   $127.40  
  Purchase #6 $133.30   9.137%   $145.4796   $145.48   $145.50   $145.50  
  Purchase #7 $18.92   8.787%   $20.5825   $20.58   $20.60   $20.60  
  7 purchase totals = $934.92       $1,026.3891   $1,026.38   $1,026.40   $1,026.40