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 $246.52   6.592%   $262.7706   $262.77   $262.75   $262.80  
  Purchase #2 $198.65   8.304%   $215.1459   $215.15   $215.15   $215.10  
  Purchase #3 $158.96   13.870%   $181.0078   $181.01   $181.00   $181.00  
  Purchase #4 $210.25   11.636%   $234.7147   $234.71   $234.70   $234.70  
  Purchase #5 $227.54   10.563%   $251.5751   $251.58   $251.60   $251.60  
  Purchase #6 $110.25   11.612%   $123.0522   $123.05   $123.05   $123.10  
  Purchase #7 $165.62   4.812%   $173.5896   $173.59   $173.60   $173.60  
  7 purchase totals = $1,317.79       $1,441.8559   $1,441.86   $1,441.85   $1,441.90