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 $87.25   9.258%   $95.3276   $95.33   $95.35   $95.30  
  Purchase #2 $160.63   9.251%   $175.4899   $175.49   $175.50   $175.50  
  Purchase #3 $225.97   7.264%   $242.3845   $242.38   $242.40   $242.40  
  Purchase #4 $14.41   10.820%   $15.9692   $15.97   $15.95   $16.00  
  Purchase #5 $237.54   13.842%   $270.4203   $270.42   $270.40   $270.40  
  Purchase #6 $206.37   8.495%   $223.9011   $223.90   $223.90   $223.90  
  Purchase #7 $29.89   12.120%   $33.5127   $33.51   $33.50   $33.50  
  7 purchase totals = $962.06       $1,057.0053   $1,057.00   $1,057.00   $1,057.00