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 $49.83   4.758%   $52.2009   $52.20   $52.20   $52.20  
  Purchase #2 $126.74   3.543%   $131.2304   $131.23   $131.25   $131.20  
  Purchase #3 $74.89   6.114%   $79.4688   $79.47   $79.45   $79.50  
  Purchase #4 $204.33   7.664%   $219.9899   $219.99   $220.00   $220.00  
  Purchase #5 $181.33   8.868%   $197.4103   $197.41   $197.40   $197.40  
  Purchase #6 $127.78   5.817%   $135.213   $135.21   $135.20   $135.20  
  Purchase #7 $221.80   10.660%   $245.4439   $245.44   $245.45   $245.40  
  7 purchase totals = $986.70       $1,060.9572   $1,060.95   $1,060.95   $1,060.90