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 $56.53   7.416%   $60.7223   $60.72   $60.70   $60.70  
  Purchase #2 $45.51   8.550%   $49.4011   $49.40   $49.40   $49.40  
  Purchase #3 $27.29   11.290%   $30.371   $30.37   $30.35   $30.40  
  Purchase #4 $207.81   9.493%   $227.5374   $227.54   $227.55   $227.50  
  Purchase #5 $60.64   13.291%   $68.6997   $68.70   $68.70   $68.70  
  Purchase #6 $220.60   4.112%   $229.6711   $229.67   $229.65   $229.70  
  Purchase #7 $181.54   8.430%   $196.8438   $196.84   $196.85   $196.80  
  7 purchase totals = $799.92       $863.2464   $863.24   $863.20   $863.20