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 $37.70   11.173%   $41.9122   $41.91   $41.90   $41.90  
  Purchase #2 $108.87   11.133%   $120.9905   $120.99   $121.00   $121.00  
  Purchase #3 $52.42   10.724%   $58.0415   $58.04   $58.05   $58.00  
  Purchase #4 $225.88   4.259%   $235.5002   $235.50   $235.50   $235.50  
  Purchase #5 $231.55   3.789%   $240.3234   $240.32   $240.30   $240.30  
  Purchase #6 $88.83   10.331%   $98.007   $98.01   $98.00   $98.00  
  Purchase #7 $150.36   13.398%   $170.5052   $170.51   $170.50   $170.50  
  7 purchase totals = $895.61       $965.2800   $965.28   $965.25   $965.20