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 $235.97   7.552%   $253.7905   $253.79   $253.80   $253.80  
  Purchase #2 $157.93   12.524%   $177.7092   $177.71   $177.70   $177.70  
  Purchase #3 $30.60   13.548%   $34.7457   $34.75   $34.75   $34.70  
  Purchase #4 $12.36   10.463%   $13.6532   $13.65   $13.65   $13.70  
  Purchase #5 $92.32   3.196%   $95.2705   $95.27   $95.25   $95.30  
  Purchase #6 $67.55   10.792%   $74.84   $74.84   $74.85   $74.80  
  Purchase #7 $233.85   9.814%   $256.8   $256.80   $256.80   $256.80  
  7 purchase totals = $830.58       $906.8091   $906.81   $906.80   $906.80