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 $92.88   5.167%   $97.6791   $97.68   $97.70   $97.70  
  Purchase #2 $164.49   13.488%   $186.6764   $186.68   $186.70   $186.70  
  Purchase #3 $192.70   6.387%   $205.0077   $205.01   $205.00   $205.00  
  Purchase #4 $67.50   8.228%   $73.0539   $73.05   $73.05   $73.10  
  Purchase #5 $31.49   9.478%   $34.4746   $34.47   $34.45   $34.50  
  Purchase #6 $241.70   10.232%   $266.4307   $266.43   $266.45   $266.40  
  Purchase #7 $107.25   4.636%   $112.2221   $112.22   $112.20   $112.20  
  7 purchase totals = $898.01       $975.5445   $975.54   $975.55   $975.60