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 $87.75   10.208%   $96.7075   $96.71   $96.70   $96.70  
  Purchase #2 $221.36   12.373%   $248.7489   $248.75   $248.75   $248.70  
  Purchase #3 $167.42   12.750%   $188.7661   $188.77   $188.75   $188.80  
  Purchase #4 $209.53   10.320%   $231.1535   $231.15   $231.15   $231.20  
  Purchase #5 $39.74   13.835%   $45.238   $45.24   $45.25   $45.20  
  Purchase #6 $62.69   4.227%   $65.3399   $65.34   $65.35   $65.30  
  Purchase #7 $27.40   5.683%   $28.9571   $28.96   $28.95   $29.00  
  7 purchase totals = $815.89       $904.9110   $904.92   $904.90   $904.90