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 $51.84   13.571%   $58.8752   $58.88   $58.90   $58.90  
  Purchase #2 $70.33   4.212%   $73.2923   $73.29   $73.30   $73.30  
  Purchase #3 $243.58   4.248%   $253.9273   $253.93   $253.95   $253.90  
  Purchase #4 $136.30   10.316%   $150.3607   $150.36   $150.35   $150.40  
  Purchase #5 $240.65   8.375%   $260.8044   $260.80   $260.80   $260.80  
  Purchase #6 $29.77   11.524%   $33.2007   $33.20   $33.20   $33.20  
  Purchase #7 $186.33   5.408%   $196.4067   $196.41   $196.40   $196.40  
  7 purchase totals = $958.80       $1,026.8673   $1,026.87   $1,026.90   $1,026.90