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 $60.91   7.111%   $65.2413   $65.24   $65.25   $65.20  
  Purchase #2 $179.99   7.748%   $193.9356   $193.94   $193.95   $193.90  
  Purchase #3 $181.66   10.651%   $201.0086   $201.01   $201.00   $201.00  
  Purchase #4 $240.94   4.565%   $251.9389   $251.94   $251.95   $251.90  
  Purchase #5 $62.69   11.619%   $69.974   $69.97   $69.95   $70.00  
  Purchase #6 $134.82   12.352%   $151.473   $151.47   $151.45   $151.50  
  Purchase #7 $39.87   8.651%   $43.3192   $43.32   $43.30   $43.30  
  7 purchase totals = $900.88       $976.8906   $976.89   $976.85   $976.80