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 $228.69   10.294%   $252.2313   $252.23   $252.25   $252.20  
  Purchase #2 $56.42   7.208%   $60.4868   $60.49   $60.50   $60.50  
  Purchase #3 $227.46   5.538%   $240.0567   $240.06   $240.05   $240.10  
  Purchase #4 $58.81   13.445%   $66.717   $66.72   $66.70   $66.70  
  Purchase #5 $145.56   8.258%   $157.5803   $157.58   $157.60   $157.60  
  Purchase #6 $189.72   7.501%   $203.9509   $203.95   $203.95   $204.00  
  Purchase #7 $51.55   3.432%   $53.3192   $53.32   $53.30   $53.30  
  7 purchase totals = $958.21       $1,034.3422   $1,034.35   $1,034.35   $1,034.40