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 $56.66   10.701%   $62.7232   $62.72   $62.70   $62.70  
  Purchase #2 $223.50   7.230%   $239.6591   $239.66   $239.65   $239.70  
  Purchase #3 $216.97   12.455%   $243.9936   $243.99   $244.00   $244.00  
  Purchase #4 $173.78   3.488%   $179.8414   $179.84   $179.85   $179.80  
  Purchase #5 $63.58   5.177%   $66.8715   $66.87   $66.85   $66.90  
  Purchase #6 $26.80   6.433%   $28.524   $28.52   $28.50   $28.50  
  Purchase #7 $43.64   10.693%   $48.3064   $48.31   $48.30   $48.30  
  7 purchase totals = $804.93       $869.9192   $869.91   $869.85   $869.90