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 $29.94   13.542%   $33.9945   $33.99   $34.00   $34.00  
  Purchase #2 $178.56   3.809%   $185.3614   $185.36   $185.35   $185.40  
  Purchase #3 $155.92   4.839%   $163.465   $163.47   $163.45   $163.50  
  Purchase #4 $223.59   13.441%   $253.6427   $253.64   $253.65   $253.60  
  Purchase #5 $101.64   7.701%   $109.4673   $109.47   $109.45   $109.50  
  Purchase #6 $147.60   6.209%   $156.7645   $156.76   $156.75   $156.80  
  Purchase #7 $225.29   3.409%   $232.9701   $232.97   $232.95   $233.00  
  7 purchase totals = $1,062.54       $1,135.6655   $1,135.66   $1,135.60   $1,135.80