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 $54.76   11.219%   $60.9035   $60.90   $60.90   $60.90  
  Purchase #2 $186.55   4.559%   $195.0548   $195.05   $195.05   $195.10  
  Purchase #3 $80.93   6.580%   $86.2552   $86.26   $86.25   $86.30  
  Purchase #4 $198.83   10.373%   $219.4546   $219.45   $219.45   $219.50  
  Purchase #5 $56.36   10.193%   $62.1048   $62.10   $62.10   $62.10  
  Purchase #6 $122.87   8.566%   $133.395   $133.40   $133.40   $133.40  
  Purchase #7 $236.88   7.864%   $255.5082   $255.51   $255.50   $255.50  
  7 purchase totals = $937.18       $1,012.6761   $1,012.67   $1,012.65   $1,012.80