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 $160.47   10.661%   $177.5777   $177.58   $177.60   $177.60  
  Purchase #2 $13.78   13.176%   $15.5957   $15.60   $15.60   $15.60  
  Purchase #3 $175.51   5.185%   $184.6102   $184.61   $184.60   $184.60  
  Purchase #4 $88.71   10.421%   $97.9545   $97.95   $97.95   $98.00  
  Purchase #5 $155.97   9.279%   $170.4425   $170.44   $170.45   $170.40  
  Purchase #6 $232.63   3.449%   $240.6534   $240.65   $240.65   $240.70  
  Purchase #7 $113.62   9.655%   $124.59   $124.59   $124.60   $124.60  
  7 purchase totals = $940.69       $1,011.4240   $1,011.42   $1,011.45   $1,011.50