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 $47.90   6.660%   $51.0901   $51.09   $51.10   $51.10  
  Purchase #2 $227.53   13.192%   $257.5458   $257.55   $257.55   $257.50  
  Purchase #3 $31.67   10.277%   $34.9247   $34.92   $34.90   $34.90  
  Purchase #4 $182.74   5.771%   $193.2859   $193.29   $193.30   $193.30  
  Purchase #5 $53.25   11.621%   $59.4382   $59.44   $59.45   $59.40  
  Purchase #6 $243.99   6.773%   $260.5154   $260.52   $260.50   $260.50  
  Purchase #7 $168.29   6.300%   $178.8923   $178.89   $178.90   $178.90  
  7 purchase totals = $955.37       $1,035.6924   $1,035.70   $1,035.70   $1,035.60