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 $62.77   9.148%   $68.5122   $68.51   $68.50   $68.50  
  Purchase #2 $237.89   7.723%   $256.2622   $256.26   $256.25   $256.30  
  Purchase #3 $169.50   7.211%   $181.7226   $181.72   $181.70   $181.70  
  Purchase #4 $110.27   5.648%   $116.498   $116.50   $116.50   $116.50  
  Purchase #5 $52.57   9.380%   $57.5011   $57.50   $57.50   $57.50  
  Purchase #6 $241.58   8.866%   $262.9985   $263.00   $263.00   $263.00  
  Purchase #7 $97.89   9.671%   $107.3569   $107.36   $107.35   $107.40  
  7 purchase totals = $972.47       $1,050.8515   $1,050.85   $1,050.80   $1,050.90