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 $54.95   6.106%   $58.3052   $58.31   $58.30   $58.30  
  Purchase #2 $151.93   7.705%   $163.6362   $163.64   $163.65   $163.60  
  Purchase #3 $9.55   8.103%   $10.3238   $10.32   $10.30   $10.30  
  Purchase #4 $238.68   6.385%   $253.9197   $253.92   $253.90   $253.90  
  Purchase #5 $149.41   12.873%   $168.6435   $168.64   $168.65   $168.60  
  Purchase #6 $158.71   11.567%   $177.068   $177.07   $177.05   $177.10  
  Purchase #7 $243.25   7.211%   $260.7908   $260.79   $260.80   $260.80  
  7 purchase totals = $1,006.48       $1,092.6872   $1,092.69   $1,092.65   $1,092.60