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 $222.67   4.613%   $232.9418   $232.94   $232.95   $232.90  
  Purchase #2 $50.83   7.490%   $54.6372   $54.64   $54.65   $54.60  
  Purchase #3 $21.25   11.409%   $23.6744   $23.67   $23.65   $23.70  
  Purchase #4 $42.77   7.672%   $46.0513   $46.05   $46.05   $46.10  
  Purchase #5 $196.50   8.770%   $213.7331   $213.73   $213.75   $213.70  
  Purchase #6 $221.27   11.151%   $245.9438   $245.94   $245.95   $245.90  
  Purchase #7 $180.74   5.145%   $190.0391   $190.04   $190.05   $190.00  
  7 purchase totals = $936.03       $1,007.0207   $1,007.01   $1,007.05   $1,006.90