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 $64.44   13.610%   $73.2103   $73.21   $73.20   $73.20  
  Purchase #2 $190.57   11.801%   $213.0592   $213.06   $213.05   $213.10  
  Purchase #3 $31.84   4.340%   $33.2219   $33.22   $33.20   $33.20  
  Purchase #4 $71.95   6.678%   $76.7548   $76.75   $76.75   $76.80  
  Purchase #5 $226.64   11.219%   $252.0667   $252.07   $252.05   $252.10  
  Purchase #6 $27.33   13.218%   $30.9425   $30.94   $30.95   $30.90  
  Purchase #7 $232.28   11.288%   $258.4998   $258.50   $258.50   $258.50  
  7 purchase totals = $845.05       $937.7552   $937.75   $937.70   $937.80