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 $48.97   11.147%   $54.4287   $54.43   $54.45   $54.40  
  Purchase #2 $56.94   9.451%   $62.3214   $62.32   $62.30   $62.30  
  Purchase #3 $168.55   9.258%   $184.1544   $184.15   $184.15   $184.20  
  Purchase #4 $123.77   12.416%   $139.1373   $139.14   $139.15   $139.10  
  Purchase #5 $160.53   8.274%   $173.8123   $173.81   $173.80   $173.80  
  Purchase #6 $101.26   8.612%   $109.9805   $109.98   $110.00   $110.00  
  Purchase #7 $205.35   4.551%   $214.6955   $214.70   $214.70   $214.70  
  7 purchase totals = $865.37       $938.5301   $938.53   $938.55   $938.50