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 $85.52   11.573%   $95.4172   $95.42   $95.40   $95.40  
  Purchase #2 $136.71   6.621%   $145.7616   $145.76   $145.75   $145.80  
  Purchase #3 $111.99   10.767%   $124.048   $124.05   $124.05   $124.00  
  Purchase #4 $116.28   6.797%   $124.1836   $124.18   $124.20   $124.20  
  Purchase #5 $202.27   5.644%   $213.6861   $213.69   $213.70   $213.70  
  Purchase #6 $42.44   4.324%   $44.2751   $44.28   $44.30   $44.30  
  Purchase #7 $242.31   4.852%   $254.0669   $254.07   $254.05   $254.10  
  7 purchase totals = $937.52       $1,001.4385   $1,001.45   $1,001.45   $1,001.50