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 $149.57   8.868%   $162.8339   $162.83   $162.85   $162.80  
  Purchase #2 $181.90   11.460%   $202.7457   $202.75   $202.75   $202.70  
  Purchase #3 $106.74   12.314%   $119.884   $119.88   $119.90   $119.90  
  Purchase #4 $222.99   10.586%   $246.5957   $246.60   $246.60   $246.60  
  Purchase #5 $65.70   5.451%   $69.2813   $69.28   $69.30   $69.30  
  Purchase #6 $112.50   13.577%   $127.7741   $127.77   $127.75   $127.80  
  Purchase #7 $92.59   5.567%   $97.7445   $97.74   $97.75   $97.70  
  7 purchase totals = $931.99       $1,026.8592   $1,026.85   $1,026.90   $1,026.80