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 $52.45   12.642%   $59.0807   $59.08   $59.10   $59.10  
  Purchase #2 $174.63   4.246%   $182.0448   $182.04   $182.05   $182.00  
  Purchase #3 $193.53   11.605%   $215.9892   $215.99   $216.00   $216.00  
  Purchase #4 $76.79   6.496%   $81.7783   $81.78   $81.80   $81.80  
  Purchase #5 $193.72   12.521%   $217.9757   $217.98   $218.00   $218.00  
  Purchase #6 $178.63   11.343%   $198.892   $198.89   $198.90   $198.90  
  Purchase #7 $109.78   9.505%   $120.2146   $120.21   $120.20   $120.20  
  7 purchase totals = $979.53       $1,075.9753   $1,075.97   $1,076.05   $1,076.00