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 $88.88   8.597%   $96.521   $96.52   $96.50   $96.50  
  Purchase #2 $35.32   13.778%   $40.1864   $40.19   $40.20   $40.20  
  Purchase #3 $163.92   7.293%   $175.8747   $175.87   $175.85   $175.90  
  Purchase #4 $24.52   8.319%   $26.5598   $26.56   $26.55   $26.60  
  Purchase #5 $166.76   13.814%   $189.7962   $189.80   $189.80   $189.80  
  Purchase #6 $199.63   6.337%   $212.2806   $212.28   $212.30   $212.30  
  Purchase #7 $194.93   3.473%   $201.6999   $201.70   $201.70   $201.70  
  7 purchase totals = $873.96       $942.9186   $942.92   $942.90   $943.00