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 $125.26   9.413%   $137.0507   $137.05   $137.05   $137.10  
  Purchase #2 $61.82   3.345%   $63.8879   $63.89   $63.90   $63.90  
  Purchase #3 $89.58   12.145%   $100.4595   $100.46   $100.45   $100.50  
  Purchase #4 $206.42   8.348%   $223.6519   $223.65   $223.65   $223.70  
  Purchase #5 $172.26   7.230%   $184.7144   $184.71   $184.70   $184.70  
  Purchase #6 $56.80   8.292%   $61.5099   $61.51   $61.50   $61.50  
  Purchase #7 $239.80   9.258%   $262.0007   $262.00   $262.00   $262.00  
  7 purchase totals = $951.94       $1,033.2750   $1,033.27   $1,033.25   $1,033.40