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 $242.43   10.300%   $267.4003   $267.40   $267.40   $267.40  
  Purchase #2 $200.56   13.824%   $228.2854   $228.29   $228.30   $228.30  
  Purchase #3 $80.59   6.664%   $85.9605   $85.96   $85.95   $86.00  
  Purchase #4 $14.56   12.615%   $16.3967   $16.40   $16.40   $16.40  
  Purchase #5 $113.91   13.407%   $129.1819   $129.18   $129.20   $129.20  
  Purchase #6 $58.58   3.525%   $60.6449   $60.64   $60.65   $60.60  
  Purchase #7 $227.27   7.845%   $245.0993   $245.10   $245.10   $245.10  
  7 purchase totals = $937.90       $1,032.9690   $1,032.97   $1,033.00   $1,033.00