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 $185.38   9.818%   $203.5806   $203.58   $203.60   $203.60  
  Purchase #2 $62.89   6.343%   $66.8791   $66.88   $66.90   $66.90  
  Purchase #3 $72.34   6.534%   $77.0667   $77.07   $77.05   $77.10  
  Purchase #4 $166.84   3.258%   $172.2756   $172.28   $172.30   $172.30  
  Purchase #5 $44.73   3.326%   $46.2177   $46.22   $46.20   $46.20  
  Purchase #6 $207.61   12.773%   $234.128   $234.13   $234.15   $234.10  
  Purchase #7 $205.53   7.261%   $220.4535   $220.45   $220.45   $220.50  
  7 purchase totals = $945.32       $1,020.6012   $1,020.61   $1,020.65   $1,020.70