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 $54.45   8.340%   $58.9911   $58.99   $59.00   $59.00  
  Purchase #2 $208.47   10.762%   $230.9055   $230.91   $230.90   $230.90  
  Purchase #3 $109.42   10.180%   $120.559   $120.56   $120.55   $120.60  
  Purchase #4 $223.31   7.333%   $239.6853   $239.69   $239.70   $239.70  
  Purchase #5 $81.72   3.438%   $84.5295   $84.53   $84.55   $84.50  
  Purchase #6 $158.51   13.731%   $180.275   $180.28   $180.30   $180.30  
  Purchase #7 $166.26   8.824%   $180.9308   $180.93   $180.95   $180.90  
  7 purchase totals = $1,002.14       $1,095.8762   $1,095.89   $1,095.95   $1,095.90