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 $192.56   11.612%   $214.9201   $214.92   $214.90   $214.90  
  Purchase #2 $79.52   11.244%   $88.4612   $88.46   $88.45   $88.50  
  Purchase #3 $212.67   13.527%   $241.4379   $241.44   $241.45   $241.40  
  Purchase #4 $155.34   6.684%   $165.7229   $165.72   $165.70   $165.70  
  Purchase #5 $222.77   7.283%   $238.9943   $238.99   $239.00   $239.00  
  Purchase #6 $215.67   8.742%   $234.5239   $234.52   $234.50   $234.50  
  Purchase #7 $52.96   6.477%   $56.3902   $56.39   $56.40   $56.40  
  7 purchase totals = $1,131.49       $1,240.4505   $1,240.44   $1,240.40   $1,240.40