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 $61.43   12.233%   $68.9447   $68.94   $68.95   $68.90  
  Purchase #2 $99.52   3.219%   $102.7235   $102.72   $102.70   $102.70  
  Purchase #3 $51.70   6.473%   $55.0465   $55.05   $55.05   $55.00  
  Purchase #4 $120.86   5.639%   $127.6753   $127.68   $127.70   $127.70  
  Purchase #5 $108.52   10.724%   $120.1577   $120.16   $120.15   $120.20  
  Purchase #6 $175.84   9.581%   $192.6872   $192.69   $192.70   $192.70  
  Purchase #7 $163.63   11.846%   $183.0136   $183.01   $183.00   $183.00  
  7 purchase totals = $781.50       $850.2485   $850.25   $850.25   $850.20