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 $134.83   11.546%   $150.3975   $150.40   $150.40   $150.40  
  Purchase #2 $110.50   12.808%   $124.6528   $124.65   $124.65   $124.70  
  Purchase #3 $46.85   12.652%   $52.7775   $52.78   $52.80   $52.80  
  Purchase #4 $180.46   3.441%   $186.6696   $186.67   $186.65   $186.70  
  Purchase #5 $244.87   4.851%   $256.7486   $256.75   $256.75   $256.70  
  Purchase #6 $116.32   5.248%   $122.4245   $122.42   $122.40   $122.40  
  Purchase #7 $208.81   3.729%   $216.5965   $216.60   $216.60   $216.60  
  7 purchase totals = $1,042.64       $1,110.2670   $1,110.27   $1,110.25   $1,110.30