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 $57.86   3.289%   $59.763   $59.76   $59.75   $59.80  
  Purchase #2 $179.90   12.152%   $201.7614   $201.76   $201.75   $201.80  
  Purchase #3 $28.37   9.552%   $31.0799   $31.08   $31.10   $31.10  
  Purchase #4 $6.35   5.501%   $6.6993   $6.70   $6.70   $6.70  
  Purchase #5 $173.91   6.847%   $185.8176   $185.82   $185.80   $185.80  
  Purchase #6 $13.35   8.132%   $14.4356   $14.44   $14.45   $14.40  
  Purchase #7 $111.71   13.670%   $126.9808   $126.98   $127.00   $127.00  
  7 purchase totals = $571.45       $626.5376   $626.54   $626.55   $626.60