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 $89.73   7.252%   $96.2372   $96.24   $96.25   $96.20  
  Purchase #2 $249.25   5.162%   $262.1163   $262.12   $262.10   $262.10  
  Purchase #3 $237.93   12.584%   $267.8711   $267.87   $267.85   $267.90  
  Purchase #4 $91.91   13.561%   $104.3739   $104.37   $104.35   $104.40  
  Purchase #5 $49.56   10.267%   $54.6483   $54.65   $54.65   $54.60  
  Purchase #6 $87.53   10.600%   $96.8082   $96.81   $96.80   $96.80  
  Purchase #7 $8.55   5.311%   $9.0041   $9.00   $9.00   $9.00  
  7 purchase totals = $814.46       $891.0591   $891.06   $891.00   $891.00