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 $168.64   13.748%   $191.8246   $191.82   $191.80   $191.80  
  Purchase #2 $64.69   12.868%   $73.0143   $73.01   $73.00   $73.00  
  Purchase #3 $205.65   12.440%   $231.2329   $231.23   $231.25   $231.20  
  Purchase #4 $41.86   11.834%   $46.8137   $46.81   $46.80   $46.80  
  Purchase #5 $67.31   5.584%   $71.0686   $71.07   $71.05   $71.10  
  Purchase #6 $206.60   5.454%   $217.868   $217.87   $217.85   $217.90  
  Purchase #7 $212.49   13.546%   $241.2739   $241.27   $241.25   $241.30  
  7 purchase totals = $967.24       $1,073.0960   $1,073.08   $1,073.00   $1,073.10