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 $114.44   8.737%   $124.4386   $124.44   $124.45   $124.40  
  Purchase #2 $245.65   3.591%   $254.4713   $254.47   $254.45   $254.50  
  Purchase #3 $30.88   8.316%   $33.448   $33.45   $33.45   $33.40  
  Purchase #4 $97.46   4.866%   $102.2024   $102.20   $102.20   $102.20  
  Purchase #5 $81.91   9.572%   $89.7504   $89.75   $89.75   $89.80  
  Purchase #6 $189.49   3.568%   $196.251   $196.25   $196.25   $196.30  
  Purchase #7 $11.95   9.645%   $13.1026   $13.10   $13.10   $13.10  
  7 purchase totals = $771.78       $813.6643   $813.66   $813.65   $813.70